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EN
In the field of ocean engineering, cavitation is widespread, for the study of cavitation nuclei transient characteristics in cavitation inception, we applied theoretical analysis and molecular dynamics (MD) simulation to study Lennard-Jones (L-J) fluid with different initial cavitation nuclei under the NVT-constant ensemble in this manuscript. The results showed that in cavitation inception, due to the decrease of liquid local pressure, the liquid molecules would enter the cavitation nuclei, which contributed to the growth of cavitation nuclei. By using molecular potential energy, it was found that the molecular potential energy was higher in cavitation nuclei part, while the liquid molecular potential energy changes greatly at the beginning of the cavitation nuclei growth. The density of the liquid and the surface layer changes more obvious, but density of vapor in the bubble changes inconspicuously. With the growth of cavitation nuclei, the RDF peak intensity increased, the peak width narrowed and the first valley moved inner. When cavitation nuclei initial size reduced, the peak intensity reduced, the corresponding rbin increased. With the decrease of the initial cavitation nuclei, the system pressure and total energy achieved a balance longer, and correspondingly, they were smaller. In addition, at the beginning of the cavitation nuclei growth, the total energy and system pressure changed greatly.
EN
It is well documented that unavoidable ions in a pulp such as Mg2+, Ca2+, and K+ have a significant effect on the interaction for particles, especially for flotation of metallic sulfide minerals and clay minerals. In this study, the effect of electrolytes on the flotation of inherently hydrophobic mineral-graphite was studied. It was found that the zeta potential showed a dramatic decrease, and the reagent adsorption capacity of mineral enhanced in the present of electrolytes. The possible mechanism responsible for improved recovery was investigated by electrokinetic, surface tension and ions adsorption tests. It is likely that the hydrophobic force is stronger than the electrostatic force due to the reduced potential of graphite. This might be in favor of the formation of hydrophobic oil film leading to an increase in the graphite floatability. The experiments provided a new spectacle to study inherently hydrophobic mineral processing with electrolyte solution.
EN
Lithium, a rare-earth element, has been in increasing demand. Spodumene flotation is an important and challenging step for lithium extraction and production from lithium ore. In the present work, flotation tests for three pure minerals (i.e., spodumene, quartz and feldspar) and a real spodumene ore were carried out at laboratory scale. The results showed that YOA, a mixture of oleic acid and dodecylamine with the molar ration of 10:1, could be used as collector to produce a spodumene concentrate with grade of 5.59% Li2O from the feed ore with grade of 1.48% Li2O where 85.24% of Li2O was recovered to the concentrate. The measured zeta potential, contact angle and adsorption capacity indicated that YOA was preferentially adsorbed on spodumene instead of on quartz or feldspar, with the spodumene surface being more hydrophobic than that of feldspar or quartz. The adsorption energies of YOA on spodumene were calculated and the results provided insights into the superior flotation performance obtained in the present work.
EN
In this paper, a continuous-time distributed algorithm is presented to solve a class of decomposable quadratic programming problems. In the quadratic programming, even if the objective function is nonconvex, the algorithm can still perform well under an extra condition combining with the objective, constraint and coupling matrices. Inspired by recent advances in distributed optimization, the proposed continuous-time algorithm described by multi-agent network with consensus is designed and analyzed. In the network, each agent only accesses the local information of its own and from its neighbors, then all the agents in a connected network cooperatively find the optimal solution with consensus.
EN
Specific emitter identification (SEI) is a technique for recognizing different emitters of the same type which have the same modulation parameters. Using only the classic modulation parameters for recognition, one cannot distinguish different emitters of a same type. To solve the problem, new features urgently need to be developed for recognition. This paper focuses on the common phenomenon of frequency drift, defines geometric features of frequency drift curve and, finally, proposes a practical algorithm of specific emitter identification using the geometric features. The proposed algorithm consists of three processes: instantaneous frequency estimation based on the adaptive fractional spectrogram, feature extraction of frequency drift curve based on geometric methods for describing a curve and recognition process based on support vector machine. Simulation results show that the identification rate is generally more than 98% above –5 dB of signal to noise ratio (SNR), and real data experiment verifies the practical performance of the proposed algorithm.
EN
Independent component analysis (ICA) is usually used as a preliminary step for maternal electrocardiogram (ECG) QRS detection in fetal ECG extraction. When applying ICA to do this, a troublesome problem arises from how to automatically identify the separated maternal ECG component. In this paper we proposed a method called PRCH (short for Peak to peak entropy, R-R interval entropy, Correlation coefficient and Heart rate) for the automatic identifying. In the method, we defined four kinds of features, including amplitude, instantaneous heart rate, morphology and average heart rate, to characterize a signal, and determined some decision parameters through machine learning. Experiments and comparison with other three existed methods were given. Through taking metric F1 for evaluation, it showed that the proposed PRCH method has the highest identifying accuracy and generalization capability.
EN
The technology for gob-side entry retaining in steep coal seams is still in the development stage. The analysis results of the caving structure of main roof, low influence of gateway’s stability because of long filling distance and weak dynamic effect of the gateway, and the low stress redistribution environment indicate that using this technology in steep coal seams has significant advantages. Moreover, to reinforce the waste rock and the soft floor and to better guard against the impact of the waste rock during natural filling, a rock blocking device and grouting reinforcement method were invented, and theoretical calculations result show that the blocking device has high safety factor. In addition, we also developed a set of hydraulic support devices for use in the strengthening support zone. Furthermore, because the retaining gateway was a systematic project, the selection of the size and shape of the gateway cross section and its support method during the initial driving stage is a key step. Thus, first, a section the size of bottom width and roof height of a new gateway was determined to meet any related requirements. Then, according to the cross sections of 75 statistical gateways and the support technique, it chosen a trapezoidal cross section when the dip of the coal seam is […], a special and an inclined arch cross section when […]. Eventually, a support system of bolts and cables combined with steel mesh and steel belts was provided. The support system used optimized material and improved parameters, can enhanced the self-bearing ability of the surrounding coal and rock masses.
PL
Technologia utrzymywania chodników w obszarze zrobów w nachylonych pokładach węgla jest nadal rozwijana i udoskonalana. Jej zastosowanie prowadzi do zawału głównego stropu, który jednak w nieznacznym tylko stopniu wpływa na stabilność chodników z uwagi na odległość obszaru podsadzania, podczas gdy oddziaływania dynamiczne na chodniki przewozowe będą niewielkie. Powstały rozkład naprężeń wskazuje, że zastosowanie tej technologii w stromych pokładach przyniesie znaczne korzyści. Ponadto, w celu wzmocnienia warstw skał płonnych i miękkich warstw spągowych, a także dla lepszego zabezpieczenia przed skutkami ruchów skał płonnych w trakcie podsadzania, opracowano urządzenia blokujące ruch skał wraz ze wzmocnieniem cementowym. Obliczenia teoretyczne wskazują że zastosowana blokada ruchów skał charakteryzuje się wysokim wskaźnikiem bezpieczeństwa. Ponadto, opracowano także zestaw wsporników hydraulicznych dla dodatkowego wzmocnienia strefy podsadzania. Z uwagi na to, że zachowanie chodnika przewozowego jest działaniem stałym i systematycznym, dobór wymiarów i kształtu przekroju chodnika oraz metody jego stabilizacji jest sprawą kluczową już na etapie drążenia chodnika. W kroku pierwszym określono więc szerokość chodnika w jego dolnej części oraz wysokość stropu zgodnie z odpowiednimi wymogami. Następnie w oparciu o wymiary przekrojów 75 statystycznych chodników oraz uwzględniając dostępne techniki stabilizacji stropu wybrano przekrój trapezoidalny gdy nachylenie pokładu węgla mieści się w przedziale […], zaś dla kątów nachylenia w przedziale […] wybrano nachylony profil łukowy. W etapie końcowym zastosowano układ stabilizujący oparty na kotwach i kablach połączonych siatka stalową i stalowymi taśmami. W systemie stabilizującym wykorzystano zoptymalizowane materiały zapewniając lepsze parametry pracy, co korzystanie wpłynie na nośność warstw górotworu w otoczeniu pokładu węgla.
EN
The study employs numerical calculations in the characterization of reservoir sandstone samples based on high-resolution X-ray computed microtomography. The major goals were to determine porosity through pore size distribution, permeability characterization through pressure field, and structure impact on rock strength by simulation of a uniaxial compression test. Two Miocene samples were taken from well S-3, located in the eastern part of the Carpathian Foredeep. Due to the relation between sample size and image resolution, two X-ray irradiation series with two different sample sizes were performed. In the first approach, the voxel side was 27 µm and in the second it was up to 2 µm. Two samples from different depths have been studied here. Sample 1 has petrophysical features of conventional reservoir deposits, in contrast to sample 2. The approximate grain size of sample 1 is in the range 0.1–1.0 mm, whereas for sample 2 it is 0.01–0.1 mm with clear sedimentation lamination and heterogenic structure. The porosity, as determined by µCT, of sample 1 is twice (10.3%) that of sample 2 (5.3%). The equivalent diameter of a majority of pores is less than 0.027 mm and their pore size distribution is unimodal right-hand asymmetrical in the case of both samples. In relations to numerical permeability tests, the flow paths are in the few privileged directions where the pressure is uniformly decreasing. Nevertheless, there are visible connections in sample 1, as is confirmed by the homogenous distribution of particles in the pore space of the sample and demonstrated in the particle flow simulations. The estimated permeability of the first sample is approximately four times higher than that of the second one. The uniaxial compression test demonstrated the huge impact of even minimal heterogeneity of samples in terms of micropores: 4–5 times loss of strength compared to the undisturbed sample. The procedure presented shows the promising combination of microstructural analysis and numerical simulations. More specific calculations of lab tests with analysis of variable boundary conditions should be performed in the future.
EN
With the development of DC distribution system within the isolated power system of a ship or an aircraft, more constant frequency loads will be supplied by inverters connected to DC main bus. In the operating mode conversion process of an isolated power system, inverters will inevitably suffer from serious disturbance and affect the stability of the system. Therefore, it is important to establish a model of the inverter that reflects its dynamic characteristics and based on which to conduct the stability analysis. This paper proposes a 12-pulse inverter model based on the generalized state space averaging (GSSA) method. This model can overcome the limitations of 12-pulse inverter state space averaging (SSA) model in transient analysis with good accuracy and fast analysis ability effectively. Three kinds of models for a 12-pulse aircraft inverter are built in MATLAB, namely GSSA model, SSA model and detail device model. The simulation results show the high accuracy of GSSA model in stability analysis. This study provides an effective analytical tool for stability analysis of 12-pulse inverter and also provides a reference for inverter modeling research of isolated power system such as in aircraft or ship.
EN
It is important to evaluate the deformation and failure of sandstone in the foundation engineering of coast, river bank and lake shore. While the deformation and failure of sandstone is a comprehensive result of energy release and dissipation, and energy release is the internal reason which leads to global failure of the sandstone. The experimental analysis is conducted on the character of energy revolution of the sandstone specimen by rating loading and unloading, and the catastrophe model is followed in analyzing elastic strain energy accumulation and release in rock deformation and failure. The index based on elastic energy release is proposed to assess the rock brittleness. It is found that increasing water content is to relieve energy release and catastrophe failure of the rock specimen, and weakening the capacity of elastic energy storage. The peak and residual values of elastic energy are raised as the confining pressure increases, and the post-peak released energy decreases progressively. The confining pressure strengthens energy storage and inhibits energy release of the rock specimen, and saturation of rock will weaken this inhibit effect. The brittleness index decreases with increasing confining pressure as the rock specimen transforming from brittle to ductile.
EN
The effect of colloidal montmorillonite (MMT) on froth flotation of graphite, galena and fluorite was investigated in this work. The results showed that the presence of sufficient amount of colloidal MMT particles in the mineral slurry would be detrimental of flotation by reducing the recovery of minerals. This observation was attributed to slime coating of MMT on the coarse valuable mineral particles and entrainment of MMT particles in the froth product together with water in the triangle froth zones. The former would reduce the recovery of the valuable minerals because of hydrophilic MMT coating. The latter would decrease the concentrate grade. The degree of slime coating depended on slurry pH, while the degree of entrainment was closely related to water recovery. It was also found that slime coating was a dominant factor in mineral flotation in acidic pH regions in the presence of colloidal MMT particles.
12
Content available remote Calibration of backward-in-time model using drifting buoys in the East China Sea
EN
In the process of oil exploitation and transportation, large amounts of crude oil are often spilled, resulting in serious pollution of the marine environment. Forecasting oil spill reverse trajectories to determine the exact oil spill sources is crucial for taking proactive and effective emergency measures. In this study, the backward-in-time model (BTM) is proposed for identifying sources of oil spills in the East China Sea. The wind, current and random walk are three major factors in the simulation of oil spill sources. The wind drag coefficient varies along with the uncertainty of the wind field, and the random walk is sensitive to various traits of different regions, these factors are taken as constants in most of the state-of-the-art studies. In this paper, a self-adaptive modification mechanism for drift factors is proposed, which depends on a data set derived from the drifter buoys deployed over the East China Sea shelf. It can be well adapted to the regional characteristics of different sea areas. The correlation factor between predicted positions and actual locations of the drifters is used to estimate optimal coefficients of the BTM. A comparison between the BTM and the traditional method is also made in this study. The results presented in this paper indicate that our method can be used to predict the actual specific spillage locations.
13
Content available remote An improved Otsu method for oil spill detection from SAR images
EN
In recent years, oil spill accidents have become increasingly frequent due to the development of marine transportation and massive oil exploitation. At present, satellite remote sensing is the principal method used to monitor oil spills. Extracting the locations and extent of oil spill spots accurately in remote sensing images reaps significant benefits in terms of risk assessment and clean-up work. Nowadays the method of edge detection combined with threshold segmentation (EDCTS) to extract oil information is becoming increasingly popular. However, the current method has some limitations in terms of accurately extracting oil spills in synthetic aperture radar (SAR) images, where heterogeneous background noise exists. In this study, we propose an adaptive mechanism based on Otsu method, which applies region growing combined with both edge detection and threshold segmentation (RGEDOM) to extract oil spills. Remote sensing images from the Bohai Sea on June 11, 2011 and the Gulf of Dalian on July 17, 2010 are utilized to validate the accuracy of our algorithm and the reliability of extraction results. In addition, results according to EDCTS are used as a comparator to further explore validity. The comparison with results according to EDCTS using the same dataset demonstrates that the proposed self-adapting algorithm is more robust and boasts high-accuracy. The accuracy computing by the adaptive algorithm is significantly improved compared with EDCTS and threshold method.
EN
A series of red-emitting phosphors InNbO4:Eu3+,Bi3+ was prepared by a high temperature solid-state reaction. The structure, size distribution and luminescence properties of the phosphors were respectively characterized by X-ray diffraction (XRD), laser particle size and molecular fluorescence spectrometer. The XRD results indicate that the phase-pure samples have been obtained and the crystal structure of the host has not changed under the Eu3+ and Bi3+ co-doping. The test of size distribution shows that the phosphor has a normal size distribution. The excitation spectra illustrate that the dominant sharp peaks are located at 394 nm (7F0→5L6) and 466 nm (7F0→5D2). Meanwhile, the emission spectra reveal that the phosphors excited by the wavelength of 394 nm or 466 nm have an intense red-emission line at 612 nm owing to the 5D0→(7F2 transition of Eu3+. Bi3+ doping has not changed the peak positions except the photoluminescence intensity. The emission intensity is related to Bi3+ concentration, and it is up to the maximum when the Bi3+-doping concentration is 4 mol%. Due to good photoluminescence properties of the phosphor, the InNbO4:0.04Eu3+,0.04Bi3+ may be used as a red component for white light-emitting diodes.
EN
On the basis of viscoelastic theory of textile material, the viscoelastic solid model consisting of a spring element and viscous element either in series or parallel is one of the most useful research models to study the mechanical behaviour of fabrics. This paper presents a method to study the bending behaviour of wool/polyester fabrics using a model consisting of the three-element model in parallel with a sliding element on the assumption that the internal frictional moment is a constant during the bending processes. From the needs of practical study, a testing method has been presented to study the bending behaviour of wool/polyester fabrics using a KES-FB3 compression tester. A comparison and analysis of the experimental results and theoretical predictions indicate that the agreement between them is satisfactory.
PL
Lepkosprężysty model bryłowy składający się z elementu sprężystego i elementu lepkiego, w układzie szeregowym lub równoległym, jest jednym z najbardziej użytecznych modeli służącym do badania mechanicznego zachowania się tkanin. W pracy przedstawiono metodę badania zachowania się zginanych tkanin wełniano-poliestrowych za pomocą modelu składającego się z trój-elementowego modelu równoległego z elementem przesuwnym przy założeniu, że wewnętrzny moment tarcia jest stały podczas procesów gięcia. Na podstawie praktycznych badań przedstawiono metodę badania zachowania się gięcia tkanin wełniano-poliestrowych przy użyciu testera kompresji KES-FB3. Stwierdzono zadowalającą zgodność między wynikami eksperymentów a przewidywaniami teoretycznymi.
EN
In this article, it aims to propose effective approaches for hydro-forming process of bi-metallic composite pipe by assuming plane strain and elastic-perfectly plastic material model. It derives expressions for predicting hydro-forming pressure and residual stress of the forming process of bi-metallic composite pipe. Test data from available experiments is employed to check the model and formulas. It shows the reliability of the proposed model and formulas impersonally.
EN
An ionospheric model and corresponding coefficients broadcasted via GNSS navigation message are generally used to estimate the time delay for single-frequency GNSS users. In this article, the capabilities of three ionospheric models, namely, Klobuchar model, NeQuick Galileo version (NeQuick G), and Neustrelitz TEC broadcast model (NTCM-BC), were assessed. The models were examined in two aspects: total electron content (TEC) prediction and ionospheric delay correction effects in single-point positioning. Results show that both NeQuick G and NTCM-BC models outperformed Klobuchar model for predicting global TEC values during all the test days. Compared with Slant TEC (STEC) along the receiver-to-satellite ray path derived from IGS global ionosphere map (GIMs), STEC from NeQuick G and NTCM-BC models tend to have less bias than those from Klobuchar model in most situations. The point positioning results were improved by applying ionospheric broadcast models especially at the mid- and low-latitude stations.
EN
The hybrid structures show excellent performance on vibration reduction for ship, aircraft and spacecraft designs. Meanwhile, the topology optimization is widely used for structure vibration reduction and weight control. The design of hybrid structures considering simultaneous materials selection and topology optimization are big challenges in theoretical study and engineering applications. In this paper, according to the proposed laminate component method (LCM) and solid isotropic microstructure with penalty (SIMP) method, the mathematical formulations are presented for concurrent materials selection and topology optimizations of hybrid structures. Thickness distributions of the plies in laminate components are defined as materials selection design variables by LCM method. Relative densities of elements in the components are defined as topology design variables by SIMP method. Design examples of hybrid 3-bar truss structures and hybrid floating raft with vibration reduction requirements verified the effectiveness of the presented optimization models.
EN
In coal mine fire rescues, if the abnormal increase of gas concentration occurs, it is the primary thing to analyze the reasons and identify sources of the abnormal forming, which is also the basis of judge the combustion state of fire area and formulate proper fire reliefs. Nowadays, related researches have recognized the methane explosion as the source of high concentration of H2 formation, but there are few studies about the conditions and reaction mechanism of gas explosion generating high concentration of H2.Therefore, this paper uses the chemical kinetic calculation software, ChemKin, and the 20L spherical explosion experimental device to simulate the generating process and formation conditions of H2 in gas explosion. The experimental results show that: the decomposition of water vapor is the main base element reaction (R84) which leads to the generation of H2.The free radical H is the key factor to influence the formation of H2 generated from gas explosion. With the gradual increase of gas explosion concentration, the explosive reaction becomes more incomplete, and then the generating quantity of H2 increases gradually. Experimental results of 20L spherical explosion are consistent with the change trend about simulation results, which verifies the accuracy of simulation analysis. The results of explosion experiments show that when gas concentration is higher than 9%, the incomplete reaction of methane explosion increases which leads to the gradual increase of H2 formation
EN
Triboelectrostatic beneficiation, as a physical method, of fly ash cannot only meet the technical requirements of fly ash application but also recycle of an unburned carbon as a useful energy source. The aim of this study was to investigate the feasibility of improving efficiency of triboelectrostatic beneficiation of wet fly ash using microwave heating. The wet fly ash with different moisture contents had an average loss-on-ignition of 12.56%. The fly ash samples were heated in a microwave oven before the experiments. The experimental conditions were electric field voltage of 40 kV and air flux ranging from 12 to 30 m3/h. The influence of the microwave heating on the wet fly ash triboelectrostatic beneficiation was discussed under the conditions of different microwave intensity and irradiation time. The results indicated that the removal rate and recycle rate of the unburned carbon showed a significant increase performance as the wet fly ash was processed by the microwave heating which was attributed to changes of moisture contents and dielectric constants caused by the microwave heating. The feasibility had been verified according to the experimental study on fly ash with different moisture contents. It can be concluded that the microwave heating process was efficiently applied for the wet fly ash triboelectrostatic beneficiation.
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