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EN
The advance of MEMS-based inertial sensors successfully expands their applications to small unmanned aerial vehicles (UAV), thus resulting in the challenge of reliable and accurate in-flight alignment for air-borne MEMS-based inertial navigation system (INS). In order to strengthen the rapid response capability for UAVs, this paper proposes a robust in-flight alignment scheme for airborne MEMS-INS aided by global navigation satellite system (GNSS). Aggravated by noisy MEMS sensors and complicated flight dynamics, a rotation-vector-based attitude determination method is devised to tackle the in-flight coarse alignment problem, and the technique of innovation-based robust Kalman filtering is used to handle the adverse impacts of measurement outliers in GNSS solutions. The results of flight test have indicated that the proposed alignment approach can accomplish accurate and reliable in-flight alignment in cases of measurement outliers, which has a significant performance improvement compared with its traditional counterparts.
EN
A coupling model between turbine blades with a varying rotating speed and oncoming vortices is constructed, where the coupling of the structure and the fluid is simulated by the van der Pol oscillation. Partial differential governing equations of motions for the coupled system are obtained and discretized by using the Galerkin method. The 1:2 subharmonic resonance and the 1:1 internal resonance are investigated with the multiple scale method and first-order averaged equations are then derived. Nonlinear responses and bifurcation characteristics are studied by a numerical integration method. Stability of bifurcation curves is determined by utilizing the Routh-Hurwitz criterion. The effect of system parameters including the detuning parameter, steady-state rotating speed, amplitude of periodic perturbation for the rotating speed and freestream velocity on vibration responses are investigated.
EN
The effects of Mg and Ca on sulfide modification of sulphur steel were studied to elucidate the difference between micromagnesium treatment and micro-calcium treatment for the inclusion of sulphur steel. The results show that the inclusions in the steel appeared with an oxide core of Al2O3 and MnS wrapped. After the addition of Mg, the core was changed to spinel, and the MnS coating was changed to Mn-Mg-S. After Ca was added, the core was changed to Ca-Al-O, and the MnS coating was changed to Mn-Ca-S. The Mg content was higher than Ca content in the sulfides of the steel. Therefore, Mg was more effective than Ca in terms of sulfide modification with the same content of Mg and Ca in steel, but the yielding rate of Mg was lower than that of Ca. The Mg content in the oxide core was higher than Mg of the coating of the inclusions in the steel treated with Mg or Mg-Ca. In contrast, the Ca content in the oxide core was lower than Ca of the coating of the inclusions in the steel treated with Ca or Mg-Ca. MnS formed and precipitated during the melt solidification process. The complex sulfide (Mg-Mn-S) was precipitated around MgO·Al2O3 in the Mg treated steel during the cooling process. CaS inclusion was precipitated on the CaO·Al2O3 inclusions in the liquid Ca-treated steel. Thus, CaS was formed first, whereas MnS was formed during the cooling process, followed by the formation of complex sulfide (CaS+MnS), which finally precipitated around CaO·Al2O3 in the Ca-treated steel.
EN
Two kinds of filler metal, Ti–Zr–Cu–Ni and Ti–Zr–Cu–Ni + Mo, were used to vacuum braze Ti2AlNb and TC4 alloys. The interfacial microstructures and the room temperature (RT) and elevated temperature shear strengths of the brazed joints were analysed. Moreover, the effects of the brazing parameters and filler metal Mo content on the microstructure and corresponding mechanical properties of the brazed joints were investigated. The results showed that the typical brazed joint mainly contained α-Ti, (Ti,Zr)2(Cu,Ni), β-Ti, and Ti-rich phases. The addition of the Mo particles was beneficial to inhibit the eutectoid transformation of β-Ti during cooling, resulting in the formation of residual β-Ti instead of α-Ti. In addition, Mo particles can also make the microstructure more homogeneous. The highest RT shear strength of the joints brazed with the Ti–Zr–Cu–Ni filler metal was 351 MPa when the joint was brazed at 980 °C for 10 min. Under the same brazing parameters, the RT shear strength reached 437 MPa with the addition of 8 wt.% Mo particles to the filler metal. Moreover, the shear strengths of the joints brazed with the Mo-free and 8 wt.% Mo filler metals tested at 600 °C were 272 MPa and 393 MPa, respectively.
EN
Seismic waves propagating through viscoelastic media experience stratigraphic absorption and attenuation effects, which directly affect the imaging resolution in seismic exploration. Without stratigraphic absorption, the ratio of deep reflection energy to shallow reflection energy (attenuation ratio) is invariable at different frequencies. If a seismogram is decomposed into different frequency bands, these signals will show similar time–energy distributions. Therefore, the attenuation ratios should be similar across different frequency bands, except for frequency-variable weights. Nevertheless, the frequencyvariable weights for different frequency bands can be obtained by benchmarking against the time–energy distributions of low-frequency information because the loss of low-frequency information is relatively insignificant. In this light, we obtained frequency-variable weights for different frequencies and established a stratal absorption compensation (SAC) model. The anisotropic basis of the shearlet enables nearly optimal representation of curved-shape seismic signals, and shearlets at different scales can represent signals for different frequency bands. Then, we combined the SAC model with the shearlet transform and established the new compensation method. As the signal and noise have different distributions in the shearlet domain, we selectively compensated the signals using a thresholding algorithm. Hence, it was possible to avoid noise enhancement. This is the prominent advantage of the proposed method over other compensation methods.
EN
Since the large amount of surface-related multiple existed in the marine data would influence the results of data processing and interpretation seriously, many researchers had attempted to develop effective methods to remove them. The most successful surface-related multiple elimination method was proposed based on data-driven theory. However, the elimination effect was unsatisfactory due to the existence of amplitude and phase errors. Although the subsequent curveletdomain multiple–primary separation method achieved better results, poor computational efficiency prevented its application. In this paper, we adopt the cubic B-spline function to improve the traditional curvelet multiple matching method. First, select a little number of unknowns as the basis points of the matching coefficient; second, apply the cubic B-spline function on these basis points to reconstruct the matching array; third, build constraint solving equation based on the relationships of predicted multiple, matching coefficients, and actual data; finally, use the BFGS algorithm to iterate and realize the fast-solving sparse constraint of multiple matching algorithm. Moreover, the soft-threshold method is used to make the method perform better. With the cubic B-spline function, the differences between predicted multiple and original data diminish, which results in less processing time to obtain optimal solutions and fewer iterative loops in the solving procedure based on the L1 norm constraint. The applications to synthetic and field-derived data both validate the practicability and validity of the method.
EN
In this study, an effective optimization approach was proposed to improve acoustical behaviors of PU foams. The important parameters of PU foams: content of water, silicone oil and catalyst A1 were chosen and their effects on sound absorption coefficient and transmission loss of PU foams were studied by using Taguchi methods. In addition, bamboo chips were incorporated into PU foams as fillers to improve the acoustical properties of PU foams. Four controlled factors: the content of water, silicone oil, catalyst A1 and bamboo chips with three levels for each factor were chosen and Taguchi method based on orthogonal array L9 (34) was employed to conduct the experiments. Based on the results of Taguchi’s orthogonal array L9 (34), signal-to noise (S/N) analysis was used and developed to determine an optimal formulation of PU-bamboo-chips foam composites.
EN
This paper describes an effective implementation of the inverse data-space multiple elimination method via the three-dimensional (3D) curvelet domain. The method can separate the surface-related operator (A) and primaries (P0) through seismic data matrix inversion. A 3D curvelet transform is introduced to sparsely represent the seismic data in the inverse data space. Hence, this approach is suitable for obtaining an accurate solution because of its multiscale and multidirectional analysis properties. The L1 norm is used to promote sparseness in the transform domain. Then, a high-fidelity separation of the operator (A) and the primaries (P0) is realized. The proposed method is applied to synthetic data from a model containing a salt structure. We compare the results with that of the traditional inverse data-space multiple elimination method and also with that of two-dimensional surface-related multiple elimination. The findings fully demonstrate the superiority of the proposed method over the traditional inverse method; moreover, the proposed method protects the primary energy more effectively than the SRME method.
EN
In many situations, the quality of seismic imaging is largely determined by a proper multiple attenuation as preprocessing step. Despite the widespread application of surface-related multiple elimination (SRME) and estimation of primaries by sparse inversion (EPSI) for the removal of multiples, there still exist some limitations in the process of prediction and subtraction (SRME) or inversion (EPSI), which make the efficiency of multiple attenuation less satisfactory. To solve these problems, a new fully data-driven method called closed-loop SRME was proposed, which combines the robustness of SRME and the multi-dimensional inversion strategy of EPSI. Due to the selection of inversion approach and constraint, primary estimation by closed-loop SRME may fall into a local optimum during the solving process, which lowers the accuracy of deep information and weakens the continuity of seismic events. To avoid these shortcomings, we first modified the solving method for closed-loop SRME to an L1 norm-based bi-convex optimization method, which stabilizes the solution. Meanwhile, in the L1 norm constraint-based optimization process, the 3D sparsifying transform, being a 2D Curvelet-1D wavelet transform, is brought in as a 3D sparse constraint. In the 3D sparsifying domain, the data become sparser, thus making the result of optimization more accurate, the information of seismic events more continuous and the resolution higher. Examples on both synthetic and field data demonstrate that the method proposed in this paper, compared with the traditional SRME and closed-loop SRME, have an excellent effect on primary estimation and suppress multiples effectively.
EN
With the wide use of AIS system in the world, especially in ports and the waters with heavy traffic, AIS message loss may be related to environmental conditions, obstacle, limitation of VHF technology and AIS network overload, thereby reducing the AIS signal successful reception rate. This paper selected typical AIS data received by Yagi and Omni antennas at the same time in specific waters, uses grid and AIS data recovery technology, establishes the AIS signal coverage model, analyzes signal reception rate of Yagi antenna and Omni antenna of AIS base station, and verified the superiority of Yagi antenna in AIS signal reception rate.
EN
Objectives: Our goal is to develop a double lumen cannula (DLC) for a percutaneous right ventricular assist device (pRVAD) in order to eliminate two open chest surgeries for RVAD installation and removal. The objective of this study was to evaluate the performance, flow pattern, blood hemolysis, and thrombosis potential of the pRVAD DLC. Methods: Computational fluid dynamics (CFD), using the finite volume method, was performed on the pRVAD DLC. For Reynolds numbers <4000, the laminar model was used to describe the blood flow behavior, while shear-stress transport k-ω model was used for Reynolds numbers >4000. Bench testing with a 27 Fr prototype was performed to validate the CFD calculations. Results: There was <1.3% difference between the CFD and experimental pressure drop results. The Lagrangian approach revealed a low index of hemolysis (0.012% in drainage lumen and 0.0073% in infusion lumen) at 5 l/min flow rate. Blood stagnancy and recirculation regions were found in the CFD analysis, indicating a potential risk for thrombosis. Conclusions: The pRVAD DLC can handle up to 5 l/min flow with limited potential hemolysis. Further modification of the pRVAD DLC is needed to address blood stagnancy and recirculation.
EN
The aim of the present study is to investigate the residual ultimate strength characteristics of box girders with variable cracks under torsional loading. A series of finite element models are established by changing the crack length and crack angle using a commercial FEA program, ABAQUS. The cracks are located at the center and torques are applied on both ends of the box beam. Different aspect ratios are considered to evaluate the effects of cracks on box beams for various widths and lengths of panels in the middle yielding region. The accuracy of the nonlinear FEA results is veri?ed by a comparison with previous predicted formulas. Based on the FEA results, the relationship between the residual ultimate strength and crack parameters can be indicated in a function with period of in the form of Fourier series.
EN
In this paper, we consider a nonparametric Shewhart chart for fuzzy data. We utilize the fuzzy data without transforming them into a real-valued scalar (a representative value). Usually fuzzy data (described by fuzzy random variables) do not have a distributional model available, and also the size of the fuzzy sample data is small. Based on the bootstrap methodology, we design a nonparametric Shewhart control chart in the space of fuzzy random variables equipped with some L2 metric, in which a novel approach for generating the control limits is proposed. The control limits are determined by the necessity index of strict dominance combined with the bootstrap quantile of the test statistic. An in-control bootstrap ARL of the proposed chart is also considered.
EN
By the soil matrix suction distribution under one-dimensional steady-state flow, soil permeability coefficient ks, infiltration intensity q and initial groundwater table factors that influence the matric suction of unsaturated soil were analyzed in this paper. Based on unsaturated soil mechanics theory, ground subsidence caused by dewatering was calculated for typical pits and the impact of non-saturated soil matrix suction value on ground subsidence was taken into consideration. The results has shown that under steady infiltration conditions (q/ks < 0), the deformation of subsidence in unsaturated zone was bigger than the initial suction with still water distribution (q/ks = 0), while under stable evaporation conditions (q/ks > 0), the deformation of subsidence in unsaturated zones was smaller than the initial suction with still water distribution. In addition, as the groundwater table was lower, the influence of distribution patterns of the initial matrix suction in unsaturated soil on deformation of ground subsidence was greater.
EN
Using vacuum evaporation and sputtering process, we prepared a photoelectric transistor with the vertical structure of Cu/copper phthalocyanine (CuPc)/Al/copper phthalocyanine (CuPc)/ITO. The material of CuPc semiconductor has good photosensitive properties. Excitons will be generated after the optical signal irradiation in semiconductor material, and then transformed into photocurrent under the built-in electric field formed by the Schottky contact, as the organic transistor drive current makes the output current enlarged. The results show that the I–V characteristics of transistor are unsaturated. When device was irradiated by full band (white) light, its working current significantly increased. In full band white light, when Vec = 3 V, the ratio of light and no light current was ranged for 2.9–6.4 times. Device in the absence of light current amplification coefficient is 16.5, and white light amplification coefficient is 98.65.
16
Content available Thermal effect on damaged stay-cables
EN
Cables may suffer severe damage in cable-stayed bridges, leading to cable relaxation and tension loss. Such a damage effect merges in the sag augmentation or tension tightened by the thermal effect. This paper is intended to investigate the static response of damaged cables coupled with the thermal effect. With the introduction of three damage parameters such as damage position, damage degree and damage range as well as temperature parameter, the dimensionless governing equations for cables are derived and the numerical method is employed to solve the nonlinear equations. The static behavior of damaged cables due to the thermal coupling effect is analyzed, and the way to remove the thermal effect is given. It shows that the aspect ratio is the major factor is the deflection of the mid-span and horizontal force in the cable, whereas the angle inclination is the next important parameter. Cables with the natural length close to the chord distance reveal the highest sensitivity to temperature, whereas pre-tensioned and non-pre-tensioned cables are less sensitive to the thermal effect. It further demonstrates that with more damage included, the sensitive scope of the variation coefficient of the axial force with aspect ratio and temperature changes dramatically.
EN
Cascaded Multi-level Inverter (CMLI) consists of H-bridge modules which can generally be divided into the one with the same DC bus voltage and another with different DC bus voltages. By using the same power devices as a standard seven-level 3H-bridge converter, the proposed converter operates with 15-level resolution, with separate DC voltage sources of voltage ratio 4:2:1. The total harmonic distortion (THD) and switching losses of the proposed hybrid cascaded converter among staircase, PWM and partial PWM control are compared with analysis and Saber simulation.
PL
W niniejszym artykule przedstawiono trzy metody modulacji dla 15-poziomowego kaskadowego falownika hybrydowego. Dokonano porównania analitycznego i symulacyjnego metod przełączania schodkowego, modulacji PWM i częściowej PWM pod względem THD oraz strat łączeń. Analiza i symulacja wyników wykazują, że proponowane metody modulacji pozwalają na uzyskanie wysokiej jakości napięcia.
EN
The Minjiang River terrace along the Longmen Shan fault zone near Wenchuan, at the eastern margin of the Tibetan Plateau, China, provides archives for tectonic activity and quaternary climate change. However, previous studies were not able to provide ages older than 100 ka due to the limitations of dating material or/and methods applied to date the fluvial sediments. In this study, we used the ESR signal of the Ti-Li center in quartz to obtain the ages of four higher terraces (T3-T6). According to the results, the terraces T3 to T6 were formed at 64±19 ka, 101±15 ka, 153±33 ka, and 423±115 ka, respectively. Combined with previous studies, these results indicate that the formations of all terraces correspond to glacial/interglacial transition periods, such as, T1-T5 being correlated to MIS2/1, MIS4/3, MIS5d/5c, and MIS6/5e respectively, while T6 probably to MIS12/11. According to these data, it is found that the average incision rate was significantly higher over the last 150 ka than that previous 100 ka (250 to 150 ka). As both tectonics and climate have affected the formation of these terraces, in addition to the overall uplifting of Tibetan Plateau, the regional uplift due to isostasy would be an additional tectonic factor in the formation of river terraces in the eastern margin of Ti-betan plateau.
19
Content available remote ESR dating of the Donggutuo Palaeolithic site in the Nihewan Basin, northern China
EN
The fluvio-lacustrine sequences in the Nihewan Basin, northern China, provide important terrestrial archives about Palaeolithic settlements and, therefore, about early human occupation in high northern latitude in East Asia. Here we present detailed ESR dating of the Donggutuo Palaeo-lithic site, located in this basin. Four levels A, B, C and E of the Donggutuo archaeological layer yield ESR ages ranging from 1060±129 ka to 1171±132 ka with a mean of 1119±132 ka. The ages are con-sistent with the paleomagnetic data, which show that the Donggutuo Palaeolithic site lies just below the onset of the Jaramillo normal subchron (0.99-1.07 Ma). Furthermore, our results indicate that the reliable ESR dating range of bleached quartz using Ti-Li centre can be effectively extended to 1100 ka and the Ti-Li centre was zeroed before the last deposition, which requires improvement of the understanding of the bleaching mechanism conditions.
20
Content available remote Numerical Study on Thermal Environment in Mine Gob Under Coal Oxidation Condition
EN
The most feared of hazards in underground mines are those of fires and explosions. This study focuses on the temperature-rising process of residual coal under spontaneous combustion condition in coal mine gob. A numerical model has been established considering the chemical reaction, heat transfer and components seepage flow. The temperature distributions and maximum values for different positrons at various times have been calculated by using the coupled model. An experimental model has been also developed for model calibration. The validation indicates the numerical model is accurate and suitable for solving the temperature-rising problem in coalmines. The simulation results show that high temperature zone appears at the air intake roadway side in the gob and enlarging the ventilation flux increases the risk of self-ignition of coal. The research results can be used to predict the temperature-rising of coal spontaneous combustion and coal resources prevention.
PL
Pożary i wybuchy stanowią największe zagrożenia w kopalniach. Opisane w pracy badania dotyczą procesów powodujących wzrost temperatury resztkowego węgla, doprowadzający do jego samozapłonu, w odpadach z kopalni. Model numeryczny sformułowano, biorąc pod uwagę reakcje chemiczne, wymianę ciepła i przepływy składników. Rozkłady temperatury i maksymalne wartości w różnych położeniach i w różnych czasach zostały obliczone z użyciem modelu sprzężonego. Do kalibracji został również opracowany model doświadczalny. Walidacja wykazała, że model numeryczny jest dokładny i odpowiedni do rozwiązania problemu wzrostu temperatury w kopalniach węgla. Wyniki symulacji wskazują, że strefa podwyższonej temperatury pojawia się na szlakach wlotu powietrza do materiału i zwiększenie strumienia wentylującego zwiększa ryzyko samozapłonu węgla. Wyniki badań mogą być wykorzystane do przewidywania wzrostu temperatury grożącego samozapłonem węgla oraz do ochrony jego zasobów.
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