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The particle morphology of granular materials comprises different characteristic scales, including particle shape and surface texture. Different methods have been proposed to characterise the morphology using three-dimensional parameters, among which is the fractal method. These methods, however, are applied either at the scale of particle shape or surface texture. A framework unifying the multi-scale morphology obtained from different measuring instruments could advance the current understanding to this topic, but is still lacking. This paper proposes a novel methodology to characterise the morphology of sand particles across different scales based on results from two previously adopted instruments with different measuring capabilities – an X-ray micro-computed tomography (μCT) and a high-resolution optical microscope equipped with an interferometer. The methodology is applied to sand-sized particles of a crushed granitic rock and a natural quarzitic sand (Fujian sand). By using spectrum analysis on data from both μCT and interferometer measurements, a single fractal dimension is found linking the spectrum of the two measurements for the crushed granitic rock. For Fujian sand, two self-affine patterns are observed, which serves as a separation between particle shape and surface texture, and also indicates that the fractal dimension obtained at larger scale may not be simply extended to small scales. The translation of surface measurements into numerically reconstructed particle morphology at particle shape and surface texture scale is demonstrated by using spherical harmonic expansion and power spectral density functions.

As cathodes, iron-series (Fe, Co, Ni) clusters supported by carbon materials exhibit outstanding electrocatalytic reduction activities in many electrocatalytic applications. To date, this general characteristic of iron-series clusters that should be related to the inherent attributes of these electrodes has not been fully understood from the perspectives of thermodynamics and electronic structure alone. Electron transport is a necessary process in electrocatalysis, and therefore, the study of the change of the electronic state in electron transport is beneficial for understanding this general characteristic of iron-series cluster catalysts. In this work, the electron transport properties, including the conductivity and transport spin-polarization at the Ni-cluster/graphene interface are carefully investigated as an example of carbon-supported iron-series electrodes. Using first-principles calculations within the framework of the nonequilibrium Green’s function density functional theory (NEGF-DFT), we reveal that the electronic transport states of the coupled Ni-cluster/graphene are strongly changed compared to those of their isolated Ni-cluster and graphene component. It is found that graphene dominates the overall conductivity of the interface, while the morphology of Ni-clusters controls the spin polarization efficiency. High spin polarization can lead to the self-excitation effect of the electrons that raises the energy of the electronic system, improves the thermodynamics of the reduction reaction and promotes catalytic activity. Our work hints that iron-series elements (Fe, Co, Ni) based electrodes may generally show transport polarization that is likely to give rise to a high electrocatalytic reduction activity and such transport polarizability can be used as a new factor in the further exploration and design for electrocatalytic materials.

In the present study, a hydraulic shock absorber is proposed. Since the damper is mainly used in suspension energy recovery system, the damping characteristics of the damper under no-load state are studied in this paper. Structural design is conducted so that the unidirectional flow of the oil drives the hydraulic motor to generate electricity. Meanwhile, an asymmetrical extension/compression damping force is obtained. A mathematical model of the shock absorber is established, and the main characteristics of the inherent damping force are obtained. Based on the established model, effects of the accumulator volume, accumulator preinflation pressure, hydraulic motor displacement, check valve inner diameter, and spring stiffness, hydraulic line length and inner diameter on the indicator characteristics are analyzed. Moreover, a series of experiments are conducted on the designed damper to evaluate the characteristics of the inherent damping force and analyze the effect of the accumulator volume and preinflation pressure on the damping characteristics.

Soil grains when treated with dimethyldichlorosilane (DMDCS) create a thin soft coating layer. The presence of such a layer changes the grain surface wettability giving desirable hydraulic properties which has great potential in engineering practice. The thickness of such a layer has been identified to be an influencing parameter for the mechanical properties. But its estimation is not straightforward as the soil grain contains a relatively rough surface which is non-negligible compared to the thin soft coating. In this paper, we proposed a method that is based on the surface topography to estimate the soft coating thickness. A high-resolution microscope equipped with a white light interferometer was employed to examine the soil grain surface. It was found that the coating thickness is largely dependent on the surface topography of soil grains. The present method, applicable for particles with a very thin coating layer that is comparable to the surface roughness, such as for natural sands, could be used to further study the effect of coatings, of synthetic or natural origin, on the hydro-mechanical behaviour of coated soil samples.

Microgrids should go into islanding operations to supply power for local critical loads in the event of grid faults. During the operation of the microgrid, the voltage of the point of common coupling (PCC) can be maintained within a certain range by energy storage equipment (ESE). In this article, a direct seamless transfer strategy is developed based on the design of the power and inductor parameters of the three-phase converter in the ESE. When unintentional islanding occurs, the amplitude and frequency of the PCC voltage is affected by the output voltage of the converter, the rated power of the converter, and the voltage drop across the inductor. To ensure the value of the amplitude and frequency of the PCC voltage within the prescribed range, limiters are added to the modulation waves to realize the direct seamless transfer strategy. By analyzing the vector diagram of voltage and current vectors for different loads, the power requirement of the ESE and the voltage drop across the inductor in the converter are obtained. Finally, the design of the limiters’ parameters, analysis of inductor ripple current, and influence of nonlinear load on the PCC voltage are presented for the proposed control strategy.

This article presents a new and fast indirect method for solving fuel-optimal descent trajectories in the gravitational field of an irregularly-shaped asteroid. The costates associated with a two-impulse descent trajectory are used as approximate costates for the costate initialization of a finite-thrust fuel-optimal trajectory planning problem. The approximate solutions of the initial velocity and mass costates are given in analytical forms. A simple shooting equation is derived to solve the approximate position costates. The two-impulsive descent trajectory is solved by an irregular gravitational Lambert solver. Based on the Lambert solver and approximate costates, an algorithm is proposed for trajectory optimization with varying time of flight. The effectiveness and efficiency of the proposed method are tested through the simulation of landing on the asteroid 433 Eros. Additionally, a computationally efficient approximate model is employed to replace the polyhedral model, which greatly improves the computational speed and enhance the ability to address uncertainties.

Current bioactive modifications of Ti-based materials for promoting osteogenesis often decrease corrosion fatigue strength (σcf) of the resultant implants, thereby shortening their service lifespan. To solve this issue and accelerate the osteogenesis process, in the present study, a TiO2 nanorods (TNR)-arrayed coating was hydrothermally grown on optimal surface mechanical attrition treated (SMATed) titanium (S-Ti). The microstructure, bond integrity, residual stress distribution, and corrosion fatigue of TNR-coated S-Ti (TNR/S-Ti) and the response of macrophages and bone marrow-derived mesenchymal stem cells (BMSCs) to TNR/S-Ti were investigated and compared with those of mechanically polished Ti (P-Ti), S-Ti, and TNR-coated P-Ti (TNR/P-Ti). S-Ti showed a nanograined layer and an underlying grain-deformed region with residual compressive stress, which was sustained even when it was hydrothermally coated with TNR. TNR on S-Ti showed nanotopography, composition, and bond strength almost identical to those of P-Ti. While TNR/P-Ti showed a considerable decrease in σcf compared to P-Ti, TNR/S-Ti exhibited an improved σcf which was even higher than that of P-Ti. Biologically, TNR/S-Ti enhanced adhesion, differentiation, and mineralization of BMSCs, and it also promoted adhesion and M1-to-M2 transition of macrophages as compared to S-Ti and P-Ti. With rapid phenotype switch of macrophages, the level of proinflammatory cytokines decreased, while anti-inflammatory cytokines were upregulated. In co-culture conditions, the migration, differentiation, and mineralization of BMSCs were enhanced by increased level of secretion factors of macrophages on TNR/S-Ti. The modified structure accelerated bone apposition in rabbit femur and is expected to induce a favorable immune microenvironment to facilitate osseointegration earlier; it can also simultaneously improve corrosion fatigue resistance of Ti-based implants and thereby enhance their service life.

As a result of the influence of clock drift and uncertainty delay in synchronous message transmission, the clock synchronization model based on statistical distribution cannot accurately describe clock deviation. This model also requires a large number of timestamp samples that cause a storage occupation issue for wireless sensor nodes with limited resources. The modeling method based on grey prediction has advantages of low sample demand and simple modeling process. However, the accuracy of the existing clock synchronization models needs to be improved. Based on the grey prediction theory, this paper proposes an adaptive fractional-order operator clock synchronization algorithm considering uncertainty delay. First, based on the clock model and clock offset model, the frequency offset between nodes is optimized by taking the mean on the clock frequencies. Second, a grey prediction algorithm based on a fractional-order operator is proposed by estimating the uncertainty delay in message transmission to obtain the clock offset. Finally, the order of the fractional-order accumulation is adjusted adaptively in the grey prediction model according to the collected timestamp sample values so that the estimation of the uncertainty delay is more accurate, thereby improving the accuracy of the clock offset. Compared with the first-order accumulative grey prediction clock synchronization algorithms and timing-sync protocol for sensor networks, the proposed scheme improved the synchronization accuracy by 29.18% and 44.01%, respectively, and reduced the variance of the clock offset by 48.66% and 64.89%. Thus, the proposed algorithm is characterized by improved stability.

Flexible transparent conductive films are indispensable for nowadays wearable electronic devices with various applications. However, existing solutions such as ITO and metal mesh were limited by their poor intrinsic stretching ability. In this work, we designed and fabricated silver nanowires (AgNWs) on graphene hybrid films for enhanced mechanical and electrical performance. In situ TEM characterizations show that, beside conductive paths, silver nanowire network, can also contribute to the toughening mechanisms of the hybrid films. Furthermore, bending and electrical tests were applied to examine the corresponding flexible electronics’ performance. Finally, we showed that the fabrication of our AgNW/graphene hybrid films could be scaled up for large film applications and extended to other 1D/2D hybrid systems.

To find a balance between energy and safety, a series of compounds based on azo-, azoxy-, 1,4,2,5-dioxadiazene-, and 3,6-diamino-1,2,4,5-tetrazine-bridged bis(aminofurazan) were designed and synthesized. These compounds were analyzed by nitro group charges (Qnitro) and bond dissociation energy (BDE) calculations, which are related to sensitivity and stability. Based on the calculated results, derivatives of 3,6-bis(3-aminofurazan-4-ylamino)-1,2,4,5-tetrazine have the largest values for -Qnitro and BDE of all of the bis(aminofurazan) compounds. This shows that compounds based on 3,6-bis(3-aminofurazan-4-ylamino)-1,2,4,5-tetrazine have the lowest sensitivities and best stabilities, which has been substantiated by experiments. Additionally, their explosive properties remain essentially competitive with compounds based on azo-, azoxy-, and 1,4,2,5-dioxadiazene-bridged bis(aminofurazan). Hirshfeld surface calculations were also performed to better understand the relationship between the molecular structure and stability/sensitivity. This work highlights the value of 3,6-diamino-1,2,4,5-tetrazine as a linker to achieve good balance between safety and energy.

This paper investigates the characteristics of lift-off velocity with analytically derived vector expression. Compared with a single asteroid system, there is an external perturbed body that has influence on the dynamic environment of the target body surface for a binary asteroid system. Binary asteroid systems modeled by ellipsoid-sphere model are classified as two cases: synchronous system and non-synchronous system. The effects of different factors on the lift-off velocity related with the dynamic characteristics of the systems are analyzed. In the synchronous system, the lift-off velocity curves are similar with those in the single asteroid system. The maximum relative difference in lift-off velocity caused by perturbed bodies of different masses is less than 8%, according to maximum and minimum lift-off velocity distributions. The density/spin parameter and ellipticity parameter have other different influences on lift-off velocity. As for a non-synchronous system, the distributions of the maximum and minimum lift-off velocity with different poses are studied and their trends for one period are summarized. The minimum lift-off velocity is found to be close to zero in the low latitude at some certain time points that are affected by the spin ratio.

Gastric cancer (GC) is the fifth most cancer type and the third most cause of cancer-associated deaths worldwide along with the 5-year survival rate is less the 30%. This investigation was aimed to synthesis the piperine-loaded zinc oxide nanocomposite (ZnO-Pip-NC) and investigating its anticancer activity against the GC by in vitro and in vivo models by the inhibiting the apoptotic and PI3K/Akt/mTOR signaling pathways. The synthesized ZnO-Pip-NC was characterized by different techniques. The cytotoxicity of zinc oxide, piperine and the formulated ZnO-Pip-NC was tested against the AGS cells by MTT assay. The intracellular ROS level, mitochondrial membrane potential, and apoptotic cell necrosis in the AGS cells was examined by fluorescent staining techniques. The expression of apoptotic and PI3K/Akt/mTOR signaling markers were inspected by western blotting and the expression of pro0inflammatory markers analyzed by RT-PCR technique. The antioxidant levels were examined by standard methods and histopathology of gastric mucosa was analyzed. The ZnO-Pip-NC treatment appreciably inhibited the AGS cell viability. ZnO-Pip-NC treated cells also exhibited excessive intracellular ROS, diminished MMP, nuclear damages, and apoptosis induction in AGS cells. The enhanced expression of pro-apoptotic proteins and inhibition of PI3K/Akt/mTOR signaling pathway was noted in ZnO-Pip-NC treated cells. In vivo studies proved that the ZnO-Pip-NC noticeably restored the antioxidants in the GC animals and also prevented the gastric mucosa and inhibited the GC tumor formation. In conclusion, the findings of this investigation confirmed the anticancer potential of ZnO-Pip-NC against the GC via inhibiting the PI3K/Akt/mTOR signaling pathway.

The ternary alloy system Ag-Cu-Si was investigated in detail for the first time. The phase diagram was analysed by means of light optical microscopy, powder x-ray diffraction, differential thermal analysis (DTA) and scanning electron microscopy in combination with energy dispersive x-ray spectroscopy. The complete isothermal section at 650 °C was studied experimentally, and several additional samples were studied in order to obtain insight into phase equilibria with the high-temperature phases of the binary Cu-Si system. DTA studies in two vertical sections were used to determine ternary invariant phase reactions and to construct the ternary reaction scheme (Scheil diagram). A liquidus surface projection was constructed by combining these data with microstructure analysis of selected as-cast samples.

Purpose The purpose of this paper is to propose cuckoo optimization algorithm (COA)-based back propagation neural network (BPNN) to reduce the effect of the nonlinearities presented in laser triangulation displacement sensors. The 3D positioning and posture sensor allows access to the third dimension through depth measurement; the performance of the sensor varies according to the level of nonlinearities presented in the system, which leads to inaccuracies in measurement. Design/methodology/approach While applying optimization approach, the mathematical model and the relationship between the key parameters in the laser triangulation ranging and the indexes of the measuring system were analyzed. Findings Based on the performance of the parametric optimization method, the measurement repeatability reached 0.5 µm with an STD value within 0.17 µm, an expanded uncertainty of measurement was within 5 µm, the angle error variation of the object’s rotational plane was within 0.031 degrees and nonlinearity was recorded within 0.006 per cent in a full scale. The proposed approach reduced the effect of the nonlinearity presented in the sensor. Thus, the accuracy and speed of the sensor were greatly increased. The specifications of the optimized sensor meet the requirements for high-accuracy devices and allow wide range of industrial application. Originality/value In this paper, COA-based BPNN is proposed for laser triangulation displacement sensor optimization, on the basis of the mathematical model, clarifying the working space and working angle on the measurement system.

In this paper, extreme learning machine (ELM) method is used to classify the faults of fuel system. Although the learning speed of ELM is fast, its classification accuracy and generalization ability need to be improved. Bat Algorithm has a strong ability of global optimization. In order to make up for the deficiency of the ELM, this paper proposes a fault diagnosis model based on an improved bat algorithm to optimize the ELM. The experimental results show that the improved bat algorithm greatly improves the classification accuracy and generalization ability of the ELM, and verifies the validity of the proposed model.

Gold nanoparticles with special surface plasmon resonance have been widely used in sensing and therapy because of their easy preparation, unique optical properties, excellent biocompatibility, etc. The applications of gold nanoparticles in chemo/biosensing, imaging, and therapy reported in 2016-2019, are summarized in this review. Regarding the gold nanoparticle-based sensing or imaging, sensing mechanisms and strategies are provided to illustrate the concepts for designing sensitive and selective detection platforms. Gold nanoparticlemediated therapy is introduced by surface plasmon resonance-based therapy and delivery-based therapy. Beyond the sole therapeutic system, platforms through synergistic therapy are also discussed. In the end, discussion of the challenges and future trends of gold nanoparticle-based sensing and therapy systems is described.

Since the demands for the thermostability of energetic materials have risen in the deep mining and aerospace industries, the research on heat-resistant explosives with remarkable thermal stability as well as high energy has always been a tough challenge. Here we present the synthesis and properties of an advanced heat-resistant explosive 5,5′-bis(3,5-dinitro-1H-pyrazol-4-yl)-1H,1′H-3,3′-bi(1,2,4-triazole) (BDBT-2). This compound exhibits a striking thermal decomposition temperature of 372 °C, a high detonation velocity of 8705 m s−1, desirable sensitivity properties, and is easy to scale-up. These impressive properties and energetic performance of BDBT-2 surpass those of the current and industrially used heat-resistant explosive 2,2′,4,4′,6,6′-hexanitrostilbene (HNS) and the recently reported thermostable explosives, strongly supporting BDBT-2 as a candidate for advanced heat-resistant explosives. Moreover, a comprehensive comparison between regioisomers 5,5′-bis(3,4-dinitro-1H-pyrazol-5-yl)-2H,2′H-3,3′-bi(1,2,4-triazole) (BDBT-1) and BDBT-2 suggests that regiochemical modulation will have broad prospects in the development of advanced heat-resistant explosives.

Under a multiscenario environment with frequent bursts of data in the edge cloud, the resource allocation in the edge cloud will affect the stability of its nodes. To address this problem, a balanced virtual resource allocation model based on conflict conditions is proposed. Based on a thorough study of the similarity between task attributes and resources used by the host, the concept of a task backlog is implemented to achieve a preliminary balanced allocation of tasks; thus, a conflict condition based on the remaining resources of the physical and virtual machines is proposed. Further, a matrix of phased conflict coefficients is built to establish a balanced virtual machine allocation model. The results of experiments comparing the performance of the proposed model with that of other existing models indicate that the proposed model can reduce the virtual machine scheduling time by up to 8.33%, save up to 6.25% of host energy consumption, and improve the algorithm efficiency by 20.47% compared with the other algorithms. To avoid the local optimal problem caused by dynamic virtual machine migration, an improved ant colony algorithm is combined with the above model, and concepts of a pheromone volatility factor and suppression factor are implemented to optimize the pheromone measurement function and ensure that the virtual machine migration path is globally optimal. Overall, the model reduces the conflict rate of resources on the physical machine and can maintain stable operation under CPU usage fluctuation, thus realizing a balanced allocation of node resources.

The patched conic method is usually used for preliminarily design of gravity-assist transfer trajectories. However, gravity assist is usually simplified as an instantaneous velocity impulse and the time of flight for gravity assist is ignored, which differs from actual scenarios. In this paper, gravity assist is considered as a continuous process and a novel method employing the pseudostate theory is proposed to design gravity-assist transfer trajectories. The mission trajectory is categorized as gravity-assist segments and interplanetary transfer segments. A powered gravity-assist model based on the pseudostate theory is used to solve the gravity-assist segments with the restricted three-body dynamics. Then, these gravity-assist segments thus solved are patched with the interplanetary transfer segments using an adaptive iterative patching technique, which adopts an adaptive parameter adjustment strategy to improve the efficiency and robustness. Thereafter, a consecutive interplanetary mission trajectory is finally obtained. In addition, a new estimation formula of the sweepback duration is derived according to the radius of gravity field and the excess velocity. The simulation results verify the effectiveness and accuracy of the proposed formula. The transfer trajectories to Jupiter with Venus, Earth and Mars gravity assists are respectively obtained by the proposed method. Compared with patched conic methods, the fuel optimal and more realistic trajectories are efficiently solved utilizing the proposed method for gravity-assist interplanetary mission.

Robust principal component analysis (RPCA) based methods via decomposition into low-rank plus sparse matrices offer a wide range of applications for image processing, video processing and 3D computer vision. Most of the time the observed imagery data is often arbitrarily corrupted by anything such as large sparse noise, small dense noise and other unknown fraction, which we call mixed noise in this paper. However, low rank matrix recovery by RPCA is born for the existence of large sparse noise, so its performance and applicability are limited in the presence of mixed noise. In this paper, a generalized robust principal component analysis with norm $$l_{2,1}$$ model is proposed to solve the problem of low-rank matrix recovery under mixed large sparse noise and small dense noise. The corrupted matrix is written as a combination that minimizes the nuclear norm, the 1-norm and the norm $$l_{2,1}$$, which has high efficiency, flexibility and robustness for low rank matrix recovery from mixed noise. Then a novel and efficient algorithm called random permutation alternative direction of multiplier method is applied to solve the model. Experiments with simulations and real datasets demonstrate efficiency and robustness of this model and algorithm.

Surface roughness plays an important role in macro and micro-scale granular behaviors; however, there is currently lack of a unified approach to quantify the roughness of closed outlines and surfaces, which can consider the overall morphological characteristics of particles. This paper proposes approaches that are suitable for roughness evaluation of 2D general-shape closed outlines and 3D general-shape closed surfaces. For 2D closed outlines, the roughness is evaluated by comparing the real outline with the benchmark outline reconstructed based on the Fourier analyses. For 3D closed surfaces, the roughness is calculated by comparing the real surface against the benchmark surface reconstructed by the spherical harmonic analyses. The local deviation as well as the overall roughness of 2D closed outlines, and 3D closed surfaces, can be evaluated via the approach. After analyzing the roughness of two types of particles with different morphological characteristics by the proposed approaches, it is found that the 2D arithmetic average roughness and the 2D root mean square roughness are well correlated, and so are their 3D counterparts. Nevertheless, values of the 2D and 3D indices are not well correlated for each type of particles, and the particles with different texture can be more clearly distinguished from each other based on the 3D roughness parameters than on the 2D counterparts.

Shale gas is a crucial unconventional natural gas; carbon dioxide is a serious greenhouse gas. Therefore, using supercritical carbon dioxide as a fracturing fluid can fracture shale reservoirs and ...

Line-structured laser scanner has been widely applied in industrial applications, such as 3D reconstruction. Breakpoint detection of the laser stripe centerline is necessary for further analysis. The laser stripe centerline is always not smooth in industrial environments due to the inevitable noises. In this paper, a robust and accurate breakpoint detection method named Fitting-Derivative-Optimization (FDO) is proposed, which mainly includes three steps. The first step is to fit the noisy laser stripe centerline. A novel piecewise fitting method without any empirical parameters is proposed in this step. The second step is to initialize the breakpoints. The second derivative curve of the point slope angle in the fitted laser stripe centerline is calculated. The local extremum points in the second derivative curve are extracted to be the initial breakpoints. The third step is to optimize the breakpoints. In this step, a new optimization method named Neighborhood-Circle (NC) is proposed, which optimizes each breakpoint in its neighborhood circularly to weaken the influence of correlation between breakpoints. Finally, robustness and accuracy of the proposed FDO method are evaluated by simulations and experiments respectively. In simulations, different Gaussian noises are added into the laser stripe centerline for comparisons. Experiments are also implemented to detect breakpoints for two industry parts by using a line-structured laser scanning system. Both of the simulation and experiment results demonstrate that the proposed FDO method can perform well in industrial environments.

Isoprothiolane (IPT) was one of the most commonly used pesticides around the world. It was reported to be the highest concentration and frequency of detection of 13 most commonly used pesticides in Mekong Delta recently. The oxidation degradation kinetic of ozone and chlorine with IPT and the identification of the degradation products was investigated in this research. The results showed that both ozone and chlorine oxidized IPT rapidly under typical water treatment condition, and that both reactions followed second order reaction kinetics. The ozone reaction rates exhibited no pH dependence with the rate constant of 247.1 (±11.0) M−1s−1 at 25 °C, whereas chlorine reaction rates increased dramatically with decreasing pH. The rate constant for hypochloric acid was 73.3 (±3.1) M−1s−1 at 25 °C, while the reaction of hypochlorite was negligible. The degradation products by chlorine and ozone were identified by LC-MS/MS and the reaction pathways were proposed. The thioether and the carbon-carbon double bond in IPT were the reactive sites during chlorine and ozone oxidation. The thioether group was oxidized into sulfoxide and further sulfone group, and the carbon-carbon double bone were cleaved to form diisopropyl ester of malonic acid, diisopropyl ester of tartronic acid and diisopropyl ester of ketomalonic acid monohydrate. Compared to ozone reaction, it was more complicated for chlorine reaction, which yielded chlorine substituted, hydroxylated and dithiolane ring-opening products.

Propagation properties of photonic crystals with defect are analyzed by the precise integration time domain (PITD) method in the paper. The precise integration is applied to the finite diff...

To ensure safe drilling with narrow pressure margins in deepwater, a new deepwater dual-gradient drilling method based on downhole separation was designed. A laboratory experiment was conducted to verify the effectiveness of downhole separation and the feasibility of realizing dual-gradient in wellbore. The calculation of dynamic wellbore pressure during drilling was conducted. Then, an optimization model for drilling parameters was established for this drilling method, including separator position, separation efficiency, injection volume fraction, density of drilling fluid, wellhead back pressure and displacement. The optimization of drilling parameters under different control parameters and different narrow safe pressure margins is analyzed by case study. The optimization results indicate that the wellbore pressure profile can be optimized to adapt to the narrow pressure margins and achieve greater drilling depth. By using the optimization model, a smaller bottom-hole pressure difference can be obtained, which can increase the rate of penetration (ROP) and protect reservoirs. The dynamic wellbore pressure has been kept within safe pressure margins during optimization process, effectively avoiding the complicated underground situations caused by improper wellbore pressure. Key words: narrow pressure margins, deepwater dual-gradient drilling, drilling parameters, optimization model, maximum drilling depth

Hydraulic fracturing is an effective treatment technology to improve reservoir permeability. In this paper, the dual effective stress was introduced into the theoretical analysis of water pressure during crack initiation, and the theoretical analysis results are about 37% more accurate than Hubbert and Willis theory based on the numerical results. Moreover, the artificial-macrocrack effects on fracturing crack propagation and direction changes have been analyzed and compared to hydraulic fracturing without the artificial-macrocrack. The water pressure required for crack initiation with the artificial-macrocracks is less than that without the artificial-macrocracks. When α (α is defined as the angle between the artificial-macrocrack and the horizontal direction) reached or exceeded π/4, crack growth began at the tip of the macrocrack with a higher box counting dimension than that at a lower values of α. Furthermore, a series of simulations have been conducted to obtain the point of fracturing crack direction change when α = 0. The fracturing crack starts to propagate at the artificial-macrocrack tip when λ = 0.95 (λ is defined as the ratio of horizontal stress to vertical stress), and the crack propagation direction becomes vertical when λ = 0.9625. By extracting the crack morphology from the simulation results, it was determined that the box-counting dimension, the crack perimeter, and the crack area proportion reach maximal values at λ = 0.95, λ = 0.9625 and λ = 0.975, respectively. Using image segmentation technology, the impact area proportion reached a maximum at λ = 0.9625 with a more effective treatment than at other values of λ. Finally, beddings and cracks in natural strata were taken into account for fracturing crack propagation, and beddings and cracks could guide the fracturing cracks. More microcracks could be generated along the beddings with the artificial-macrocrack effect at λ = 0.9. Case study indicated that the gas extraction achieved high production in the first 40 days, and the field data with fracturing treatment show that the average pure gas flux is about 4 times greater than that without fracturing. This research also provides a new idea to mine intact rock of construction aggregate.

This paper aims to investigate the wellbore thermal behavior in multi-gradient drilling (MGD). Based on the principle of energy conservation, a synthetic transient heat transfer model was established, in which the mass and heat transfer of lightweight glass microspheres (GMSs) were considered for the wellbore fluid region, and the dynamic variation in the moving boundary was considered for the drill bit and separator region. The synthetic model was solved using the combination of finite volume method and dynamic laying method. The accuracy and capability of the model were verified using field measurement data and previous typical models. The calculation results suggested that the annular temperature near the separator dropped suddenly due to the mass and heat transfer of GMSs. Additionally, the dynamic drilling of the drill bit would increase the bottomhole temperature continuously. Furthermore, a sensitivity analysis indicated that when the GMS concentration increased from 5% to 45%, the annulus temperature at the separator reduced by 9.15%; when the distance between the drill bit and separator increased from 1100 m to 3000 m, the bottomhole temperature increases by 3.99%; and the effect of the separator number on annulus temperature combined the dual role of separator position and GMS concentration.

Gold nanoclusters (Au NCs) with atomic precision have huge application potentials in chemo/bio sensing, catalysis, and energy conversion. However, a precise atomic control of Au NCs still remains a great challenge. Herein, we developed a facile one-pot and top-down strategy to synthesize eight-atom numbered Au NCs (Au8 NCs), aiming to understand their fundamental physicochemical properties and explore their potential applications. The etching of gold nanoparticles by their encapsulated hyperbranched polyethyleneimine was significantly promoted by a newly proposed catalyst, hydrogen peroxide, which gave rise to brightly blue-emitting Au8 NCs (quantum yield = 28.8%). The as-prepared Au8 NCs could sense hemoglobin with a detection limit of 5.0 nM through the combination of Fenton reaction and fluorescence resonance energy transfer. And the sensing behaviour is unaffected by the presence of various interferents such as proteins, small molecules, anions, and metal ions. In addition, a hemoglobin evaluation in blood samples with small relative standard deviations and satisfied recoveries was achieved using the proposed Au8 NC nanoprobes.

Projected future changes in mean precipitation over Thailand based on multi-model regional climate simulations of CORDEX Southeast Asia

The formation of chlorinated by-products is a major concern associated with electrochemical water treatment processes. This study investigated the formation of chlorinated by-products during surface water treatment by a newly developed electrochemical advanced oxidation process (EAOP), the electro-peroxone (E-peroxone) process, which couples ozonation with in situ electro-generation of hydrogen peroxide (H2O2) from cathodic oxygen reduction. Due to the enhanced ozone (O3) conversion to hydroxyl radicals (•OH) by electro-generated H2O2, the E-peroxone process considerably accelerated the abatement of ozone-refractory micropollutants such as clofibric acid and chloramphenicol in the selected surface water compared to conventional ozonation. In addition, the cathodically generated H2O2 effectively quenched hypochlorous acid (HOCl) derived from the anodic oxidation of chloride in the surface water. Therefore, the formation of trichloromethane (TCM) and chloroacetic acids (CAAs) from the reactions of HOCl with dissolved organic matter (DOM) was insignificant during the E-peroxone process, and similar levels of TCM and CAAs were generally observed in the conventional ozonation and E-peroxone treated water. In contrast, considerable amounts of HOCl could be generated from the anodic oxidation of chloride and then accumulated in the surface water during conventional electrolysis process, which resulted in significantly higher concentrations of TCM and CAAs in the electrolysis treated water. The results of this study suggest that the E-peroxone process can overcome the major limitation of conventional electrochemical processes and provide an effective and safe EAOP alternative for micropollutant abatement during water treatment.

Early gas kick detection is an important measure to ensure well control safety. In accordance with the fluctuation of the bottomhole pressure during early gas kick, the gas kick can be detected rapidly and early with downhole measurement tool. At present, erroneous diagnosis often occurred when gas kick detection was performed using pressure fluctuations of a single measured point. In this paper, firstly, considering the water hammer effect, a wellbore pressure fluctuation model at the initial stage of gas kick was established to accurately describe the transient annular pressure variations. The model was solved using the composite difference scheme and was verified using a laboratory gas kick experiment. Secondly, a dual-measured-points (DMP) method for early gas kick detection was presented based on the consistencies and discrepancies of bottomhole pressures at two measured points. The distance between two measured points was optimized. Simulation results indicated that the annular pressure at the measured point increased and periodically changed with time in the initial stage of gas kick, and then declined approximately linearly after the gas-liquid interface reached the measured point. The distance between the two measured points was mainly dominated by the borehole diameter, and increased with the decrease of borehole diameter. The gas kick confirmation time (GKCT) obtained using DMP method was 2–7 min and the corresponding gas kick confirmation volume (GKCV) was 0.3–0.5 m3. The GKCT diminished with the increase of the formation permeability and bottomhole negative differential pressure, and with the decrease of the borehole diameter and well depth.

As part of its Paris Agreement commitment, China pledged to peak carbon dioxide (CO2) emissions around 2030, striving to peak earlier, and to increase the non-fossil share of primary energy to 20% by 2030. Yet by the end of 2017, China emitted 28% of the world’s energy-related CO2 emissions, 76% of which were from coal use. How China can reinvent its energy economy cost-effectively while still achieving its commitments was the focus of a three-year joint research project completed in September 2016. Overall, this analysis found that if China follows a pathway in which it aggressively adopts all cost-effective energy efficiency and CO2 emission reduction technologies while also aggressively moving away from fossil fuels to renewable and other non-fossil resources, it is possible to not only meet its Paris Agreement Nationally Determined Contribution (NDC) commitments, but also to reduce its 2050 CO2 emissions to a level that is 42% below the country’s 2010 CO2 emissions. While numerous barriers exist that will need to be addressed through effective policies and programs in order to realize these potential energy use and emissions reductions, there are also significant local environmental (e.g., air quality), national and global environmental (e.g., mitigation of climate change), human health, and other unquantified benefits that will be realized if this pathway is pursued in China.

In this study, a three-dimensional mathematical model was used to study the contribution of clathrins during the process of cellular uptake of spherical nanoparticles under different membrane tensions. The clathrin-coated pit (CCP) that forms around the inward budding of the cell membrane was modeled as a vesicle with bending rigidity. An optimization algorithm was proposed for minimizing the total energy of the system, which comprises the deforming nanoparticle, receptor–ligand bonds, cell membrane, and CCP, in which way, the profile of the system is acquired. The results showed that the CCP enable full wrapping of the nanoparticles at various membrane tensions. When the cell membrane tension increases, the total deformation energy also increases, but the ratio of CCP bending to the minimum value of the total energy of the system decreases. The results also showed that the diameter of the endocytic vesicles determined by the competition between the stretching of the cell membrane and confinement of the coated pits are much larger than the nanoparticles, which is quit different as the results in passive endocytosis that is not facilitated by the CCPs. The present results indicate that variations of tension on cell membranes constitutes a biophysical marker for understanding the size distribution of CCPs observed in experiments. The present results also suggest that the early abortion of endocytosis is related to that the receptor–ligand bonds cannot generate adequate force to wrap the nanoparticles into the cell membrane before the clathrins respond to support the endocytic vesicles. Correspondingly, late abortion may relate to the inability of CCPs to confine the nanoparticles until the occurrence of the necking stage of endocytosis.

This Paper presents a fast homotopy method for solving fuel-optimal asteroid landing trajectories. Similar to the traditional homotopy method, the fuel-optimal control problem is connected with the...

Surface texture plays an important role in understanding the mechanical and hydraulic behavior of a soil but has drawn little attention, especially for three dimensional parameters. Currently, the few studies on measurements and quantification of surface texture are limited to sand sized particles. To date, the surface texture of sand has been successfully obtained by using a high-resolution optical microscope for a given measurement area that is small and comparable to the sand particle size. However, for larger particles, such as gravel, the larger surface area may create difficulties. For instance, as the particle size increases, the surface texture could be influenced by other factors such as the mineral composition, scale-dependent fabric and others, hindering the simple extension of a method that quantifies the surface texture of sand to gravel. This paper attempts to address this challenge by proposing a method to measure and quantify the surface texture of gravel which explicitly takes into account the different texture scales. Crushed granite is taken as the testing material. To explore the surface texture at different scales, a 3D laser scanner (at millimeter scale) and a high resolution optical microscope equipped with interferometry (at micro-meter scale) have been employed. The novel method defines and quantifies the surface texture of gravel with the aid of the power spectral density function (PSD) and a fractal method. It was found that the fractal dimension at the two different scales do not coincide, which might be interpreted as two different self-affine patterns of the surface. For example, the features of single minerals (e.g. fractures, cleavage, hardness) dominate at the small scale and become less prominent at the large scale where grain size and shape prevail. When a single fractal dimension from PSD at the large scale is assumed for both scales, the associated error can be quantified using the square root of the surface height to a mean plane and is found to be within 15%. This suggests that the surface texture examined at a large scale by using the 3D laser scanner could be representative of the gravel, though cautions should be taken in individual cases for any quantitative studies of the effect of the surface texture.

A simultaneous high rejection of trace organic compounds (TrOCs) and low rejection of divalent cations (Ca2+/Mg2+) would be desirable for nanofiltration (NF) applied for drinking water treatment. The target was however not attainable by using the currently available commercial NF membranes. In this study, 3,5-diaminobenzoic acid (BA) was used as an additional diamine monomer besides piperazine (PIP) to prepare novel thin film composite NF membranes via interfacial polymerization with trimesoyl chloride (TMC). A series of NF membranes were prepared by varying BA to PIP concentration ratios in order to obtain a proper membrane pore size and a sufficiently high negative surface charge density. Membrane characterizations and performance tests showed that the incorporation of BA could increase the pore size, enhance the negative surface charge and change the structural properties of the membrane, which in turn affected the membrane water permeability and separation performance. The optimal membrane prepared with a BA/PIP ratio of 50%:50% exhibited a low rejection of CaCl2 (25.8%) and MgCl2 (32.0%) in single salt solutions at 10 mmol/L and a moderate rejection of Ca2+/Mg2+ ions ( 80%) for six out of eight selected pharmaceuticals (PhACs). The ATR-FTIR spectra and XPS analysis showed that BA could interfere the polymerization between PIP and TMC in forming the membrane active layer while the cross-linking degree between BA and TMC was relatively low. This implied that the proposed treatment target could also be achieved by using some other acidic diamines with similar functionalities of BA.

Accurate prediction of the wellbore temperature is critical to achieve pressure control in controlled gradient drilling. In accordance with the mass, momentum, and energy conservation principles, an integrated heat transfer model was developed for eight distinct interconnected thermal regions by considering the coupled heat and mass transfer of hollow balls, as well as the dynamic rock breaking of the drill bit. The finite volume method was employed to solve differential equations, and the dynamic layering method was employed to update the geometry and number of mesh adjacent to the moving boundary. The validity of the integrated model was verified using measured field temperatures. Using this model, the impacts of dynamically increasing well depth and mechanical energy of the drill bit on the bottomhole temperature during the dynamic drilling were compared. Additionally, the variations in temperature distribution characteristics and heat transfer efficiency, caused by the heat and mass transfer of hollow balls, were investigated. Furthermore, a sensitivity analysis of the temperature characteristics and heat transfer efficiency to the hollow ball concentration, and the position and number of cyclone separators was conducted.

Haloacetaldehydes (HALs) are the third prevalent group of disinfection by-products (DBPs) by weight in drinking water, and their cytotoxicity and genotoxicity are higher than regulated DBPs. In order to understand their formation mechanism during chlorination and ozonation-chlorination, this study examined the reaction kinetics of chloral hydrate (CH), dichloroacetaldehyde (DCA), chloroacetaldehyde (CA) and acetaldehyde by chlorine at different pH values and chlorine doses. The results showed that the reaction rate constants increased with pH and chlorine dose, except that the degradation of CH would not be affected by the presence of free chlorine. At the same pH and chlorine dose, the half-lives of CH, DCA, CA and acetaldehyde were in the order of CH > acetaldehyde ≫ DCA > CA. A kinetic model used to predict the formation of HALs and chloroform during chlorination of acetaldehyde was developed, and the predicted data fitted well with the measured data. As pre-ozonation could oxidize natural organic matter to acetaldehydes, the concentration of acetaldehyde formed after pre-ozonation was used to calculate the HAL yields during ozonation-chlorination by the kinetic model, which fitted the experimental results well. The kinetic model elucidated that the formation mechanism of HALs was a stepwise substitution process on the α-hydrogen of acetaldehyde during chlorination.

With the expansion of urban area and population, air pollution in many areas is becoming more and more serious. PM 2.5 has the characteristics of complexity and randomness, because its concentration is affected by many factors. Researchers usually input a large number of data into random forest, Neuro-Fuzzy model or neural network model for prediction. However, there are many factors affecting PM 2.5 , some factors can promote the production of PM 2.5 , while other factors may hinder its production. In the process of training, these factors will not only bring extra noise to the prediction, but also increase the complexity of training. In this study, a method for predicting PM 2.5 concentration based on Multi-Input LSTM model was proposed. First, we design a Multi-Input LSTM model, and then the features are divided into two groups through the Spearman's rank correlation coefficient, which can be used as auxiliary input to LSTM, and add attention mechanism to reduce the noise in the data, and extract valuable features. The experimental results show that this method achieves 97.3% accuracy on the dataset better than the baseline method.

Based on the fast development of Internet and big data, how to pick out a high-quality service composition quickly from large qualities of services, and meet users’ needs have become a hotspot in service composition research. Service composition optimization is a classic NP hard problem. A modified Beetle Antennae Particle Swarm Algorithm was proposed in this paper and it was applied in web service composition optimization. The author introduced Beetle Antennae Searching Algorithm into the modified Particle Swarm Algorithm, modified position update formula, adopted the modified Nonlinear Dynamic Trigonometric Learning Factors to control the particles’ expanding capacity and global convergence capability and incorporated the modified Secondary Oscillation factors which increased the searching precision of the algorithm and global searching ability. The experimental results under real data set indicated that the modified Beetle Antennae Particle Swarm Algorithm proposed in this paper could settle large-scale web service composition optimization problems in cloud environment, had good global searching ability, comparatively faster convergence speed and needed less time cost.

The technique of tracking a non-cooperative manoeuvring satellite is important for Space Situation Awareness (SSA). However, the classical extended Kalman filter cannot work successfully in this situation. Motivated by this problem, a novel Extended Kalman Filter with Input Detection and Estimation (EKF/IDE) method is proposed in this paper for tracking a non-cooperative satellite with impulsive manoeuvres. The impulsive manoeuvre is modelled as an unknown acceleration without any prior information. An unbiased minimum-variance input and state estimation method is introduced to estimate the manoeuvre acceleration. An approach based on the Mahalanobis distance of the manoeuvre estimate error is proposed for manoeuvre detection. With the impulsive manoeuvre being detected and estimated accurately, an adaptive extended Kalman filter is proposed to estimate the state of the target. An approach of covariance inflation is proposed to deal with the manoeuvre during the unobserved period. Simulations and Monte Carlo experiments are implemented to demonstrate the feasibility and validity of the proposed method. The results of simulations show that the proposed method can accurately detect and estimate unknown impulsive manoeuvres of a non-cooperative satellite. Through the compensation of the estimated manoeuvre, the estimation of position and velocity after the manoeuvre maintains the accuracy of the pre-manoeuvre period, demonstrating the robustness of the proposed method against unknown manoeuvres.

A novel oxygen-rich energetic compound, 3-trinitromethyl-4-nitro-5-nitramine-1H-pyrazole (5), was obtained by one-step nitration of 2-(3-amino-1H-pyrazol-5-yl)acetic acid (4). Compound 5 was characterized by IR and NMR spectroscopy, elemental analysis and differential scanning calorimetry (DSC). Additionally, the structure of compound 5 was further confirmed by X-ray crystallography. Compound 5 has a high density (1.90 g cm−3), positive heat of formation (0.99 kJ g−1) and positive oxygen balance (24.8%). The calculated detonation velocity (D = 9124 m s−1) and pressure (P = 37.2 GPa) are superior to those of RDX (D = 8795 m s−1, P = 34.9 GPa). The calculated specific impulse of compound 5 (262 s) is higher than that of AP (157 s) and ADN (202 s). The combination of these attractive properties makes it a promising high energy density oxidizer.

Crystal engineering has prompted the development of energetic materials in recent years. Obtaining an explosive crystal with an ideal crystal shape and a single polymorph with high packing density and stability needs to be further studied. This work reports the synthesis, structure and energetic properties of picrylhydrazone and indazole derivatives. We presented a cyclization reaction in which the twist structure picrylhydrazones (4 and 6) with a disordered crystal packing style was converted into planar structure indazole derivatives (5 and 7) with a face-to-face crystal packing style. Compared to picrylhydrazones 4 and 6, the indazole derivatives 5 and 7 exhibited increases of 0.04 and 0.05 g cm−3 (2.4%, 2.8%), 0.07 and 0.39 kJ g−1 (3.3%, 19.3%), 341 and 309 m s−1 (4.3%, 3.7%), 2.5 and 2.9 GPa (10.9%, 11.7%), 82 and 127 K (17.9%, 27.5%), 9 and 7 J (37.5%, 31.6%) and 64 and 29 N (25.4%, 11.0%) in density, heat of formation (ΔfH), detonation velocity (D) and pressure (P), decomposition temperature (Tdec), impact sensitivity (IS) and friction sensitivity (FS), respectively. According to the experimental results and theoretical calculations, the structure–property relationship was demonstrated. Among target compounds, indazole derivative 7 exhibits an acceptable detonation performance and good sensitivity (Tdec = 316 °C, IS = 27 J, D = 8518 m s−1). This study enriches future prospects for the molecular design and crystal engineering of energetic materials.

In order to guarantee the water quality of reclaimed water in pipeline system, a chlorine bulk-decay model is required for simulation and prediction of chlorine profiles in networks. Conventional chlorine decay models of drinking water are not applicable to reclaimed water due to its complex and varying water quality. In this study, the chlorine decay of reclaimed water was investigated under different operational conditions. Based on these results, different chlorine-reactive substances (CRSs) in reclaimed water were quantified by total chlorine demand (TCD), instantaneous chlorine demand (ICD) and lasting chlorine demand (LCD), respectively. A stoichiometric model (CRS model) of chlorine decay of reclaimed water was established using ICD, TCD and reaction rate constant (k) as key independent parameters. The experimental data were fitted to the CRS model with promising results under various initial chlorine concentrations (3–10 mg-Cl2/L) and temperatures (8–35 °C). The ICD, TCD and k of different reclaimed water samples were in the range of 0.23 to 2.85 mg-Cl2/L, 1.07 to 4.73 mg-Cl2/L, and 0.04 to 4.06 L/(mg·h), respectively. Furthermore, the ICDs, TCDs and k could be determined directly by measuring the chlorine consumption at 5 min (ΔCCl,5min) and 8 h (ΔCCl,8h) after the addition of chlorine into reclaimed water, and the UV254 of reclaimed water, respectively. The relationships between ICD, TCD, k and the corresponding water quality indexes were further validated. In this way, the chlorine decay profile of reclaimed water could be predicted rapidly and precisely by measuring the ΔCCl,5min, ΔCCl,8h, and UV254 of reclaimed water.

New derivatization reactions of 1,1-diamino-2,2-dinitroethylene (FOX-7) are explored, which afford three cyclic triazinane-based energetic compounds 1, 2 and 3 featuring the FOX-7 backbone. Their structures were characterized by X-ray single crystal diffraction analysis. Among them, compound 1 shows a high detonation performance (vD: 8899 m s−1, P: 35.83 GPa) comparable to that of FOX-7. Compound 2 exhibits a good detonation performance (vD: 8332 m s−1, P: 26.47 GPa) and good thermal stability (Td = 188 °C), which is superior to that of most FOX-7-derived energetic compounds. Both of them inherit the low-sensitivity characteristic of FOX-7 because of strong inter- and intra-molecular hydrogen bonds. The presented derivatization reaction has contributed to the ever-expanding chemistry of FOX-7.

Gem/trinitro-1,2,4-triazole-functionalized azo-furazan and its derivatives were synthesized by incorporating polynitro-1,2,4-triazoles in dense energetic azo-furazan. These energetic compounds were fully characterized by NMR spectroscopy, IR spectroscopy, elemental analysis and differential scanning calorimetry. The structures of 3 were further confirmed by single-crystal X-ray diffraction. The detonation properties, determined from the calculated heats of formation and measured densities, showed that all compounds possessed high energetic performances (vD > 8049 m s−1, P > 28.4 GPa). Furthermore, 8 (vD = 9354 m s−1, P = 39.2 GPa) was superior to the highly energetic explosive HMX (vD = 9144 m s−1, P = 39.2 GPa). The safety parameters associated with impact and friction sensitivities were investigated by using BAM, which showed the insensitive nature of compounds 6 (IS = 27.5 J, FS = 360 N) and 7 (IS = 22.0 J, FS = 240 N) and the rational sensitivities of 5 and 8 (IS > 4.9 J, FS > 160 N).

Among energetic materials, there is a significant challenge faced by researchers to seek an optimal balance between high performance and safety. By combination of furoxan and 1,2,4-oxadiazole backbones and C–NO2 moieties, a promising energetic molecule, bis(4-nitro-1,2,5-oxadiazole-2-oxid-3-yl)-azo-1,2,4-oxadiazole (6), was prepared and characterized by IR, multinuclear NMR spectroscopy, elemental analysis, DSC measurements and single crystal X-ray diffraction. It has a high density (1.92 g cm−3), an acceptable thermal stability (182 °C) and a high heat of formation (1188.8 kJ mol−1/2.8 kJ g−1). The calculated detonation performance (D = 9666 m s−1 and P = 42.8 GPa) is comparable to that of CL-20 (9706 m s−1 and 45.2 GPa). More importantly, it shows desirable impact and friction sensitivity (IS: 12 J and FS: 180 N), which is less sensitive than HMX (IS: 7.4 J and FS: 120 N). Furthermore, a detonation test of compound 6 was conducted. The results indicate that compound 6 is more powerful than the commonly used secondary explosive RDX (D = 8795 m s−1 and P = 34.9 GPa). The combination of advanced performances and desirable safety makes this substance a potential secondary explosive.

The Scheimpflug imaging system has been widely applied in many fields, such as 3D reconstruction and tomographic PIV. Modeling and calibration are essential steps for further analysis of the Scheimpflug imaging system. In this paper, lens distortion model of the Scheimpflug imaging system is established and simplified for calibration. Firstly, lens distortion model of the Scheimpflug imaging system is analyzed and established, which is proved to be different from the conventional imaging system. Secondly, the established lens distortion model is simplified to reduce the complexity of the calibration for the infinite parameters. The application condition of the simplified lens distortion model is also analyzed. Finally, calibration experiment is implemented for the Scheimpflug imaging system with the simplified lens distortion model. The high calibration accuracy verifies that the simplified lens distortion model is feasible.

Fluoroquinolones (FQs) are very ubiquitous in water environment in China. The commonly application of free available chlorine (FAC) during water treatment stimulated the focus on the transformation of FQs during chlorination. Among these FQs, norfloxacin (NOR) and ofloxacin (OFL) are the representatives of secondary amine FQs and tertiary amine FQs, respectively. To better understand the difference between secondary amine FQs and tertiary amine FQs during chlorination, reaction kinetics, products and mechanisms were determined. The maximum kapp of NOR were four orders of magnitude higher than that of OFL. Moreover, eleven products of NOR and twelve products of OFL were obtained by LC-MS/MS analysis. For the two FQs, the common reactive sites were three nitrogen atoms, benzene ring, carboxyl group and double bond by chlorination. For OFL, the ether ring was also active in aqueous system. The formation mechanisms of these products were presented in this study. The main reaction pathways were electrophilic addition to nitrogen, nucleophilic substitution to benzene ring, halodecarboxylation of carboxyl group and hydrolysis of ether ring. Na2S2O3 as a reducing agent had large effect on the chlorination of secondary amine FQ, but no effect on tertiary amine FQ. Be different to secondary amine FQ, the opening of quinolone ring happened in tertiary amine FQ after halodecarboxylation of carboxyl group.