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The 3D flow filling process of LOX (Liquid Oxygen) dome is studied in a liquid oxygen/methane rocket engine. The volume, flow field pressure and velocity distributions of liquid oxygen at different time are determined. The flow property of propellant and the injection characteristic time of liquid oxygen are obtained. The results show that when the LOX dome has not been filled, the LOX flow state is disorder, and flows around the annular wall in the middle dome. The static pressure near the equalizing orifice near the liquid oxygen inlet is high and the velocity is slow. When the LOX filling is completed, the pressure at the outlet of each equalizing orifice is the same. The liquid oxygen flow is in a stable state, and the flow rate decreases. The overall velocity distribution is more uniform. In addition, in the filling process of LOX dome, the time of arrival in each area is different. There are different injection delays in each area on the injection panel, and the time of arrival of liquid oxygen in the opposite area of the inlet section of LOX dome is the latest. This result leads to the inhomogeneity of injection characteristic time and flow rate in thrust chamber.

G-quadruplexes (GQs) are guanine-rich, non-canonical nucleic acid structures that play fundamental roles in biological processes. Their structure and function are strongly influenced by their hydration shells. Although extensively studied through various experimental and computational methods, hydration patterns near DNA remain under debate due to the chemically and topologically heterogeneous nature of the exposed surface. In this work, we employed all-atom molecular dynamics (MD) simulation to study the hydration patterns of GQ DNA. The Drude oscillator model was used in MD simulation as a computationally efficient method for modeling electronic polarization in DNA ion solutions. Hydration structure was analyzed in terms of radial distribution functions and high-density three-dimensional hydration sites. Analysis of hydration dynamics focused on self-diffusion rates and orientation time correlation at different structural regions of GQ DNA. The results show highly heterogeneous hydration patterns in both structure and dynamics; for example, there are several insular high-density sites in the inner channel, and ‘spine of water’ in the groove. For water inside the loop, anomalous diffusion is present over a long time scale, but for water around the phosphate group and groove, diffusion becomes normal after ∼ 30 ps. These essentially correspond to deeply buried structural water and strong interaction with DNA, respectively.

The existing transformer short-circuit test equipment and technology have several limitations. The purpose of short-circuit test is to simulate the test of high-voltage equipment under the short-circuit fault condition of the power system, usually, a large capacity test such as transformer burst short-circuit test, circuit breaker dynamic heat stability test, to verify the reliability and stability of related equipment under extreme working conditions. At present, the large capacity test generally uses methods of power grid dedicated line power supply and short-circuit testing alternator group. However, these two methods have difficulties in construction approval, high investment costs, complex site requirements, a large impact on the power grid, and low control accuracy. Theoretical studies on equivalent simulation verification method of short-circuit withstand capability test of distribution transformer demonstrated the feasibility of using modern power electronics and advanced energy storage technology to replace conventional power grid dedicated line power supply, short-circuit testing alternator and other short-circuit impact test equipment. It could complete the transformer short-circuit impact test specified by (IEC60076-5) with lower cost and higher efficiency, verify the short-circuit impact resistance of the transformer, and improve the test capacity.

The recent discovery of the novel boron-framework in boron-rich metal borides with complex structures and intriguing features under high pressure has stimulated the search into the unique boron-network in the metal monoborides or boron-deficient metal borides at high pressure. Herein, based on the particle swarm optimization algorithm combined with first-principles calculations, we thoroughly explored the structural evolution and properties of TiB up to 200 GPa. This material undergoes a pressure-induced phase transition of Pnma → Cmcm → Pmmm. Besides of two known phases Pnma and Cmcm, an unexpected orthorhombic Pmmm structure was predicted to be energetically favored in the pressure range of 110.88–200 GPa. Intriguingly, the B covalent network eventually evolved from a one-dimensional zigzag chain in Pnma-TiB and Cmcm-TiB to a graphene-like B-sheet in Pmmm-TiB. On the basis of the microscopic hardness model, the calculated hardness (H v) values of Pnma at 1 atm, Cmcm at 100 GPa, and Pmmm at 140 GPa are 36.81 GPa, 25.17 GPa, and 15.36 GPa, respectively. Remarkably, analyses of the density of states, electron localization function and the crystal orbital Hamilton population (COHP) exhibit that the bonding nature in the three TiB structures can be considered as a combination of the B–B and Ti–B covalent interactions. Moreover, the high hardness and excellent mechanical properties of the three TiB polymorphs can be ascribed to the strong B–B and Ti–B covalent bonds.

Compared with TiN coating and TiAlN coating, the TiAlSiN superhard coating has more outstanding comprehensive properties. However, the TiAlSiN superhard coating has different physical properties from the substrate, which causes large internal stress at the interface, and reduces the bonding strength of the coating and the substrate. In this paper, according to the design criteria of nano-micron multilayer structure coating, a multilayer gradient TiAlSiN coating is designed to improve the bonding strength of TiAlSiN superhard coating, and studying the bonding strength and mechanical properties after high temperature oxidation of TiAlSiN multilayer gradient coatings prepared by cathodic arc ion plating. The results show that the designed multilayer gradient structure TiAlSiN coating has four layers: TiN layer, TiAlN layer, TiAlSiN layer and TiSiN layer. The bonding strength of the TiAlSiN multilayer gradient coating conforms to the industrial grade HF1 and it maintains good bonding properties and mechanical properties in a high temperature environment below 1000°C. It is expected to provide reference for the study and design of improving the bonding strength of the coating.

Both experimental and simulated studies of microdischarge (MD) are carried out in a dielectric barrier discharge with a pin-to-pin gap of 3.5 mm, ignited by a sinusoidal voltage with a peak voltage of 10 kV and a driving frequency of 5 kHz. Statistical results have shown that the probability of the single current pulse in the positive half-period (HP) reaches 73.6% under these conditions. Experimental results show that great luminous intensity is concentrated on the dielectric surface and the tip of the metal electrode. A 1D plasma fluid model is implemented by coupling the species continuity equations, electron energy density equations, Poisson equation, and Helmholtz equations to analyze the MD dynamics on the microscale. The simulated results are in good qualitative agreement with the experimental results. The simulated results show that the MD dynamics can be divided into three phases: the Townsend phase, the streamer propagation phase, and the discharge decay phase. During the streamer propagation phase, the electric field and electron density increase with the streamer propagation from the anode to the cathode, and their maximal values reach 625.48 Td and 2.31 × 1019 m−3, as well as 790.13 Td and 3.58 × 1019 m−3 in the positive and negative HP, respectively. Furthermore, a transient glow-like discharge is detected around the anode during the same period of streamer propagation. The formation of transient glow-like discharge is attributed to electrons drifting back to the anode, which is driven by the residual voltage in the air gap.

The shape and structure of retinal layers are basic characteristics for the diagnosis of many ophthalmological diseases. Based on B-Scans of optical coherence tomography, most of retinal layer segmentation methods are composed of two-steps: classifying pixels and extracting retinal layers, in which the optimization of two independent steps decreases the accuracy. Although the methods based on deep learning are highly accurate, they require a large amount of labeled data. This paper proposes a single-step method based on transformer for retinal layer segmentation, which is trained by axial data (A-Scans), to obtain the boundary of each layer. The proposed method was evaluated on two public data sets. The first one contains eight retinal layer boundaries for diabetic macular edema, and the second one contains nine retinal layer boundaries for healthy controls and subjects with multiple sclerosis. Its absolute average distance errors are 0.99 pixels and 3.67 pixels, respectively, for the two sets, and its root mean square error is 1.29 pixels for the latter set. In addition, its accuracy is acceptable even if the training data is reduced to 0.3. The proposed method achieves state-of-the-art performance while maintaining the correct topology and requires less labeled data.

High-speed airbreathing engines has been going on for more than a century, since French engineer Reina Lauren first developed the concept of the ramjet. Kelvin-Helmholtz (K-H) instability and compressibility effects on the evolution of supersonic mixing layer growing rate have been widely investigated in experimental and computational ways. The present study proposed a quasi-DNS solver which is written in Fortran 90, the mixing process of the supersonic planar mixing layers is analyzed in detail, especially, the process of the vortex rolling up, stretching, pairing and merging are also reported in present study. It is noteworthy that the mechanisms of K-H instability are analysed in detail, and the baroclinic term has a great influence on the growth of the supersonic mixing layer in confined space.

Streamer-to-spark transition and hydrodynamic expansion in a three-electrode pulsed surface dielectric barrier discharge are studied under atmospheric-pressure air. Three sequential discharge processes of the primary streamer, transitional streamer and spark phase during a single pulse are observed from the time-resolved plasma morphologies. The primary streamer and transitional streamer phases, with a rising voltage and low current, followed by a spark phase with a rapidly falling pulse and ascending current are characterized. Images of the discharge development show that the transitional streamer is maintained in the ionization channel after the primary streamer bridges the high-voltage electrode and the second grounded electrode. When the transitional streamer develops to a certain level, the streamer discharge transfers into the spark discharge. As a result, two shock waves are induced in the two exposed electrode domains, and then merge into a single ellipse during the process of hydrodynamic expansion. Boltzmann plots indicate that the electron temperature is 4.815 eV in the initial phase of spark discharge and gradually decreases in the spark phase. Stark broadening of the O atomic line shows that the electron density is 7.06 × 1017 cm−3 during the spark phase.

We demonstrate the dynamical properties of a vector vortex optical field (VVOF) in a strongly nonlocal nonlinear medium (SNNM) with sine and cosine parity-time-symmetric potentials (SCPT) by using the coupled vector Snyder-Mitchell model. Our study shows that the shape of the optical field is chaotically distorted in different propagation distances due to the modulation of complex refractive index. Despite the distorted optical field, the VVOF reciprocally evolves in a periodic stretch and shrink behavior during propagation in the SNNM-SCPT. The reciprocal conversions between the linear and circular polarizations periodically occur during propagation. The evolution of VVOF and the linear and circular polarization conversions are strongly dependent on the modulation of the complex refractive index, the initial powers and the vortex topological charge numbers. These results can provide a new way to complexly manipulate the VVOF in a SNNM-SCPT.

In this work, a knife-shaped gliding arc discharge (GAD) reactor driven by a modulated pulse power supply was used to convert CO2. The discharge image, voltage and current waveforms of GAD were recorded experimentally. The effects of gas flow rate, input voltage, and the duty cycle of power supply on CO2 conversion were studied. A CO2 conversion of 3.8% and energy efficiency of 39.6% could be achieved. Compared with other non-thermal plasmas, GAD has a slightly lower CO2 conversion but higher energy efficiency. In addition, the capacity of CO2 treated by GAD (6 L/min) was significantly higher than other non-thermal plasmas (e.g. 25 mL/min-125 mL/min in corona discharge and dielectric barrier discharge).

Tumor angiogenesis has been identified as an important factor in the development and progression of tumors, and anti-angiogenesis therapy has been recognized as an effective tumor therapy pattern. The unique characteristics of nanodiamonds (NDs) have been explored for photothermal therapy (PTT) against cancer, while the efficiency of mild PTT mediated by bare NDs was limited. The combination of different therapies into a single nanoplatform has shown great potential for synergistic cancer treatment. In this investigation, we integrated hydrophobic antiangiogenesis agent combretastatin A4 (CA4) into the protamine sulfate (PS) functionalized NDs hybrids (NDs@PS) with a noncovalent self-assembling method (CA4-NDs@PS) for potential combined anti-angiogenesis and mild photothermal therapy in liver cancer. The resulted CA4-NDs@PS NDs exhibited high drug loading ability, good dispersibility and colloidal stability. The near-infrared (NIR) laser irradiation could trigger the release of CA4 from CA4-NDs@PS NDs and elevate the temperature of CA4-NDs@PS NDs aqueous sulution. In vitro results illustrated that CA4-NDs@PS coupled with laser irradiation could remarkably enhance HepG-2 cells killing efficiency, leading to an enhanced photocytotoxicity. Furthermore, in vivo experiments revealed that CA4-NDs@PS exhibited a highly synergistic anticancer efficacy with NIR laser irradiation in HepG-2 tumor-bearing mice. Altogether, our present study fabricated a novel NDs@PS-based nanoplatform for combined anti-tumor angiogenesis and mild PTT against liver cancer.

A simple and facile light managing strategy has been proposed in this work to promote the light harvest in inverted perovskite solar cells (PSCs). Effective light managing structures are realized on the substrate back surface by assembling two-dimensional hexagonal closely packed (2D-HCP) SiO2 nanoparticles with different diameters. The 100 nm 2D-HCP SiO2 structure, which mainly benefits from the graded refractive index along the light incident route, possesses an effective reflectance reduction of more than 10% in a wide incident angle range. Consequently, the efficiency of inverted PSCs has been substantially improved from 17.24% to 19.12%.

In order to increase the compatibility between underwater robots and the underwater environment and inspired by the coconut octopus’s underwater bipedal walking, a method was proposed for bipedal walking for an underwater soft robot based on a spring-loaded inverted pendulum (SLIP) model. Using the characteristics of octopus tentacles rolling on the ground, a wrist arm was designed using the cable-driven method, and an underwater SLIP bipedal walking model was established, which makes an underwater soft robot more suitable for moving on uneven ground. An underwater bipedal walking soft robot based on coconut octopus was then designed, and a machine vision algorithm was used to extract the motion information for analysis. Experimental analysis shows that the underwater bipedal walking robot can achieve an average speed of 6.48 cm s−1, and the maximum instantaneous speed can reach 8.14 cm s−1.

The abnormal heat fault of marine motor frequently occurs for the bad working environment. And the navigation safety and reliability of the ship had been affected seriously. The heat transfer path of the motor is analyzed theoretically from the point of view of heat transfer in order to solve this problem. The relationship between the surface temperature and the internal temperature is established. The surface temperature of the motor is measured in real time by the temperature acquisition module. And the measurement results are transmitted to the host computer through RS485 communication interface. The inner and outer surface temperature quantitative relationship is used to judge whether the inner temperature of the motor is abnormal or not, and the real-time alarm is carried out to realize the thermal protection of the motor.

In order to solve the traffic problems and the needs of users’ safe driving, according to the requirements of the function of the Vehicle Ad-hoc Network (VANET), this paper designs and implements the application function of VANET based on the onboard unit (OBU) terminal in Android system. The design selects ARM development board as OBU terminal and uses Android operating system to design UI interface according to functional modules to interact with users. The key issues and technologies are designed and improved, which implement the security application based on security message processing and expand the non-security application, so as to achieve the purpose of assisting users to drive safely.

In the present work, a magnetic-assisted DC superimposed nanosecond-pulsed streamer discharge (DC-NPSD) with a 0.4 T parallel magnetic field is developed that achieves good performance for ozone production and toluene degradation. The influence of the assisted parallel magnetic field on the electrical characteristics, streamer propagation behavior, reactive species generation and plasma chemical properties of the DC-NPSD are systematically investigated. The experimental results indicate that better impedance matching of a nanosecond pulsed power supply and a discharge reactor can be realized by superimposing DC voltage (U DC), which facilitates reactive species production and toluene degradation. The discharge current, input energy and reactive species production can be further enhanced by the application of a parallel magnetic field under different pulse and DC voltage conditions. There are two distinct streamer phases in the DC-NPSD: a primary streamer (PS) with longer propagation distance and higher propagation velocity and a secondary streamer (SS) with shorter propagation distance and lower propagation velocity. The propagation velocities of both the PS and the SS increase with increasing U DC. Only PS propagation velocity is accelerated by a parallel magnetic field; however, that of the SS remains almost constant with or without a magnetic field. Both ozone generation and toluene degradation performance are improved by a magnetic field, which is attributed to the lengthened electron motion path under the action of Lorentz force and the constraint effect on energetic electrons in the presence of a parallel magnetic field.

In this paper, a novel approach using HPLC-MS/MS (high performance liquid chromatography-tandem mass spectrometry) was established for the identification of Pericarpium Citri Reticulatae (PCR). The identities of the components were researched by comparing the mass spectra and retention times with those of reference compounds and mass fragments with those of the known compounds published in literature. Based on the proposed strategy, ten constituents were identified. The established HPLC-MS/MS method could identify the major constituents in PCR with high efficiency and sensitivity. The new method would be suitable for the chemical identification of main components from Pericarpium Citri Reticulatae.

G-quadruplexes (GQs) are guanine-rich, non-canonical nucleic acid structures that play fundamental roles in biological processes. The topology of GQs is associated with the sequences and lengths of DNA, the types of linking loops, and the associated metal cations. However, our understanding on the basic physical properties of the formation process and the stability of GQs is rather limited. In this work, we employed ab initio, molecular dynamics (MD), and steered MD (SMD) simulations to study the interaction between loop bases and ions, and the effect on the stability of G-quadruplex DNA, the Drude oscillator model was used in MD and SMD simulations as a computationally efficient manner method for modeling electronic polarization in DNA ion solutions. We observed that the binding energy between DNA bases and ions (K+/Na+) is about the base stacking free energies indicates that there will be a competition among the binding of M+-base, H-bonds between bases, and the base-stacking while ions were bound in loop of GQs. Our SMD simulations indicated that the side loop inclined to form the base stacking while the loop sequence was Thy or Ade, and the cross-link loop upon the G-tetrads was not easy to form the base stacking. The base stacking side loop complex K+ was found to have a good stabilization synergy. Although a stronger interaction was observed to exist between Cyt and K+, such an interaction was unable to promote the stability of the loop with the sequence Cyt.

Plastic waste is spread at an unprecedented speed due to the rapid use of domestic and industrial plastic items. The environmental pollution resulting from the continued disposal of plastic wastes in landfills has not only created land problems but has also heightened the pollution of marine resources. This paper aims to review and investigate the feasibility of utilizing plastic waste in making construction bricks. The use of plastic waste in making the sand-plastic bricks will enhance the protection of the environment from the effects of plastic waste that normally takes several millennials to degrade. Thermostatic plastic waste; that is, those polymers whose recycling may not affect the environment, including polyethylene (PE) and polyethylene terephthalate (PET), is found to implore lightweight, durable, cost-effective, and low thermal conductor bricks. Compressive strength (CS) and water absorption tests are found as the key test methods for measuring the effectiveness of high-volume content of plastic waste in bricks. Notably, a high percentage of plastic waste in proportion to sand is found to improve the compressive strength of the bricks besides allowing negligible water to seep through.

This study aims to demonstrate a low-cost camera-based radioluminescence imaging system (CRIS) for high-quality beam visualization that encourages accurate pre-treatment verifications on radiation delivery in external beam radiotherapy. To ameliorate the optical image that suffers from mirror glare and edge blurring caused by photon scattering, a deep learning model is proposed and trained to learn from an on-board electronic portal imaging device (EPID). Beyond the typical purposes of an on-board EPID, the developed system maintains independent measurement with co-planar detection ability by involving a cylindrical receptor. Three task-aware modules are integrated into the network design to enhance its robustness against the artifacts that exist in an EPID running at the cine mode for efficient image acquisition. The training data consists of various designed beam fields that were modulated via the multi-leaf collimator (MLC). Validation experiments are performed for five regular fields ranging from 2 × 2 cm2 to 10 × 10 cm2 and three clinical IMRT cases. The captured CRIS images are compared to the high-quality images collected from an EPID running at the integration-mode, in terms of gamma index and other typical similarity metrics. The mean 2%/2 mm gamma pass rate is 99.14% (range between 98.6% and 100%) and 97.1% (ranging between 96.3% and 97.9%), for the regular fields and IMRT cases, respectively. The CRIS is further applied as a tool for MLC leaf-end position verification. A rectangular field with introduced leaf displacement is designed, and the measurements using CRIS and EPID agree within 0.100 mm ± 0.072 mm with maximum of 0.292 mm. Coupled with its simple system design and low-cost nature, the technique promises to provide viable choice for routine quality assurance in radiation oncology practice.

Facial expression recognition is widely used in various research fields. For facial expression recognition problems, deep neural network methods have a complex structure and poor interpretability, while traditional machine learning methods have less plentiful diverse features and low recognition rates. Therefore, a new Multilayer Convolution Sparse Coding (MCSC) method is proposed for facial expression recognition. The MCSC method deeply extracts the salient features of the human face through a convolutional neural network. Furthermore, it uses a multilayer sparse coding to learn layer by layer to recognize different facial expression features based on sparse coding, which improves the recognition accuracy of facial expressions. Finally, the MCSC method was validated on three public facial expression datasets, i.e. JAFFE, CK +, and Fer2013. We also compared and analyzed 5 feature extraction approaches. The results show that MCSC has the best facial expression recognition performance in the comparison algorithm. Its accuracies of the three data sets reach to 90.8%, 98.2%, and 72.4%, respectively.

This paper proposes a 2D-LC-ESPRIT localization algorithm based on Massive MIMO, aiming at the problem of high computational complexity caused by positioning accuracy caused by abundant antenna array resources. Firstly, the antenna matrix is partitioned, then the received signals are superposition and dimensioned. And then the eigenvalues and corresponding eigenvectors are obtained by solving the cross-covariance matrix. Finally, simulation results show that the performance of the proposed algorithm is improved compared with the traditional two-dimension ESPRIT algorithm.

Chaotic system can be used to detect weak signal in strong noise background, but is the detection performance of chaotic system prior to the detection performance of FFT? The signals under the same noise power and the same signal-to-noise ratio are detected by FFT and chaotic detection system, and the detection rate is compared by introducing the concept of detection rate of chaotic system. The results of analysis show that the detection performance of FFT is only related to the signal-to-noise ratio (SNR) with the same signal length and noise power. And the signal can be detected accurately when the SNR is -40dB, but it can’t be detected when the SNR is -60dB and -80dB. The signal can be detected sometimes, sometimes can’t be detected by the chaotic system in the same condition. Therefore, the detection probability of weak signal exists when the weak signal detected by chaotic oscillator.

To determine the effect of total nitrogen on the physical and mechanical properties and deformation characteristics of soil, samples were tested in the laboratory after being soaked in deionized water and different concentrations of nitrogen solution. The results indicate that the total nitrogen content has a significant influence on soil characteristics. Specifically, the plasticity index, specific gravity and effective cohesive strength of the samples decrease and the effective friction angle increases with increases in the total nitrogen concentration of the solution. The strain hardening phenomenon is observed in the stress-strain relationship, and the variation of the stress-strain curve of samples soaked in deionized water and nitrogen solution are highly similar. The peak shear strength of the samples initially decreased and then increased with increases in the total nitrogen concentration of the solution. The mineral composition, particularly the composition of clay minerals, is affected by the interaction with total nitrogen in the soil, leading to changes in the soil macro-characteristics.

Based on a general variational principle, Einstein-Hilbert action and sound facts from geometry, it is shown that the long existing pseudotensor, non-localizability problem of gravitational energy-momentum is a result of mistaking different geometrical, physical objects as one and the same. It is also pointed out that in a curved spacetime, the sum vector of matter energy-momentum over a finite hyper-surface can not be defined. In curvilinear coordinate systems conservation of matter energy-momentum is not the continuity equations for its components. Conservation of matter energy-momentum is the vanishing of the covariant divergence of its density-flux tensor field. Introducing gravitational energy-momentum to save the law of conservation of energy-momentum is unnecessary and improper. After reasonably defining "change of a particle's energy-momentum", we show that gravitational field does not exchange energy-momentum with particles. And it does not exchange energy-momentum with matter fields either. Therefore, the gravitational field does not carry energy-momentum, it is not a force field and gravity is not a natural force.

To study how the Cd/As flux ratio affects the microstructure and transport properties for Cd3As2 films, we used molecular beam epitaxy (MBE) to grow Cd3As2 (224) thin films on CdTe (111)/GaAs (001) virtual substrates. The effects of Cd/As flux ratio, during the grown process, on the electrical properties and surface morphology of the sample was studied. The films grown at lower Cd/As flux ratio have higher electron mobility and longer effective dephasing length. With decreasing Cd/As flux ratio, the magnetoresistance (MR) of the film changes from negative to positive. These results show that a lower beam ratio is beneficial to improve the crystal quality. In order to optimize the electrical properties of the films, the effect of annealing on the electron mobility and MR have been studied. After annealing, the MR changes from negative to positive, the electron mobility increase by 8 times, and the MR increase from 15% to 360% at 9 T. These results indicate that annealing is an effective method to optimize the electrical properties of Cd3As2 epitaxial films.

Pisha Sandstones are widely distributed in the wind-water erosion intersection zone of northwestern China. In this region, serious soil and water loss has caused the riverbed of the lower Yellow River to become higher than the adjacent ground. Fifty-two samples of four types of Pisha Sandstones (purple, white, pink and gray) from different depths (0 m, 2 m and 10 m) were examined in laboratory experiments to gain a better understanding of the relationship between erosion and the loss of Pisha Sandstones as well as the mechanisms of erosion. All of the samples were analyzed using chemical methods, X-ray diffraction and scanning electron microscopy. The mineral and chemical compositions of Pisha Sandstones were found to be very different from those of ordinary soil and varies greatly during the whole erosion process (sampling depth). Wind-water erosion also affected the microstructure between the deep and surface Pisha Sandstones, ultimately causing gravitational erosion and the loss of Pisha Sandstones. Although not all of the observations could be explained, it was apparent that wind erosion, water erosion and gravitational erosion had both direct and indirect effects on the loss of Pisha Sandstones.

This paper firstly analyses the export situation of the Pearl River Delta urban agglomeration in the past 10 years, and then uses the DEA model and panel data model to analyse export efficiency measurement and influencing factors of Pearl River Delta urban agglomeration. Finally, it proposes countermeasures to promote the improvement of the export efficiency of the Pearl River Delta urban agglomeration.

This paper has measured the level of collaborative innovation of science and technology in the Pearl River Delta urban agglomeration from 2010 to 2018 by using the DEA-Malmquist index model. The empirical results show that the overall level of technological collaboration and innovation in the Pearl River Delta urban agglomeration is relatively high. The pure technical efficiency value of the Pearl River Delta urban agglomeration has hit its peak. In terms of its scale efficiency, that of Zhuhai and Jiangmen still has room for improvement, while that of other cities has reached the optimal level. Then, through the establishment of a panel data model of the Pearl River Delta urban agglomeration from 2009 to 2018, the influencing factors of technology collaborative innovation in the Pearl River Delta urban agglomeration was analyzed. Finally, this proposal was made.

A three-dimensional geometric model was established by ANSYS ICEM according to the structure of a plate heat exchanger. And the thermodynamic performance under different working conditions is simulated. The pressure field, temperature field, velocity field and flow pattern were analyzed based the simulated results. The heat transfer performance and resistance performance of heat exchanger under different flow rates and inlet temperature difference of cold and hot fluids are compared and analyzed. The results provide support for the more efficient use of plate heat exchangers under different working conditions.

Non-metallic pipe is widely used in oilfield development in recent years because of its excellent corrosion resistance. In this paper, the wetting properties of the plastic alloy tube surface based on the contact angle of crude oil in some oil fields in Xinjiang Oilfield were experimentally studied. The wettability of the plastic alloy tube surface and its influence on the flow resistance were discussed. The wettability of metal surfaces was compared. This experimental study is helpful for the oilfield to make reasonable pipe selection.

Plastic alloy pipes and glass steel pipes are two widely used non-metallic pipes. In this paper, sliced paraffin was used to perform waxing and peeling experiments on the lining surfaces of two types of pipes, investigating the effects of temperature and wax thickness on the surface peeling force of two types of pipe line. This experimental study has certain guiding effect on the selection of non-metallic pipes and the design of the wax removal device.

Pyramidal SnO/CeO2 nano-heterojunction photocatalysts were successfully synthesized via a facile hydrothermal method. The structural characterization was investigated by using common characterization tools. The content of SnO affected the morphology and photocatalytic performance of the SnO/CeO2 nano-heterojunctions. With the increase of the SnO content, the morphology of the samples changed from a spherical structure to a pyramidal structure. The photocurrent of the SnO/CeO2 (1:6) sample was about 36 times that of pure CeO2. With SnO/CeO2 (1:6) as the photocatalyst, the degradation rate of tetracycline (TC) was 99% within 140 min under visible light and after five cyclic tests the photocatalytic efficiency of TC remained at 98%, which suggests that the SnO/CeO2 (1:6) nano-heterojunction had a high photocatalytic efficiency and stable photocatalytic performance. These results indicate that SnO/CeO2 (1:6) nano-heterojunction possesses broad prospects for industrial application.

All locating one unknown node requires at least four reference nodes in a three-dimensional space. If three reference nodes are used, then at least two places can satisfy the result of positioning in a wireless sensor network. Hence, on the basis of the boundary of sea level, the reference nodes are on the sea level below, whereas the unknown nodes are above. Here, we determine the solution of positioning both unknown and reference nodes with different spatial locations to find three reference nodes that are noncollinear and are the nearest to one unknown node. The experiment proves the accuracy of positioning with three reference nodes, which are furnished by the boundary of sea level. We conclude that the method of positioning that only uses three reference nodes can exactly realize the position and simultaneously increase the speed of positioning.

Strained HgTe thin films are typical three-dimensional topological insulator materials. Most works have focused on HgTe (100) films due to the topological properties resulting from uniaxial strain. In this study, strained HgTe (111) thin films are grown on GaAs (100) substrates with CdTe (111) buffer layers using molecular beam epitaxy (MBE). The optimal growth conditions for HgTe films are determined to be a growth temperature of 160°C and an Hg/Te flux ratio of 200. The strains of HgTe films with different thicknesses are investigated by high-resolution x-ray diffraction, including reciprocal space mapping measurements. The critical thickness of HgTe (111) film on CdTe/GaAs is estimated to be approximately 284 nm by Matthews’ equations, consistent with the experimental results. Reflection high-energy electron diffraction and high-resolution transmission electron microscopy investigations indicate that high-quality HgTe films are obtained. This exploration of the MBE growth of HgTe (111) films provides valuable information for further studies of HgTe-based topological insulators.