Search

The design of active robust controller based on delay state compensation for a class of flexible air-breathing hypersonic vehicles with input delays is described in this paper. Due to high dynamic characteristics of hypersonic vehicle, the strong uncertainties, high nonlinearity, strong coupling and control input time delays are challenging problems in the design of its control system. Therefore, it is necessary to design a control method that can handle input time delays. Finally, in this paper, the mathematical expression of the altitude nonlinear control theory problem of an aircraft with input time delay is given. Secondly, based on the backstepping method, the time delay compensation controller is designed. Thirdly, the backstepping method and dynamic control surface are used to design altitude angle control law. The stability and time delay compensation effect are proved. Finally, simulation results show that the suggested method can improve the stability and disturbance rejection performance for the system effectively, which has certain actual application value. [ABSTRACT FROM AUTHOR]

Artificial supercavitation is one of the most prospective technique for underwater drag reduction, but it still faces some unsolved roadblocks, like cavity stability, noise, power etc. This article aims at investigating the instability of cavity with the strong jet impingement, and analyzing jet behavior in restricted space. A multiphase model using coupled VOF and level set method is adopted to capture the gas-liquid interface. By changing the position of jet nozzle exit and the jet intensity, a series of numerical simulation is performed. Firstly the transient evolution of the cavity interface under the effect of the high-speed jet is obtained. Numerical model is validated by comparing with the experimental data. Then the criterion to determine the transition between different jet/cavity interaction mechanisms is established based on a non-dimensional distance parameter. Furthermore, the entrainment mechanism inside the cavity is analyzed and provides useful insights on enhancing the cavity stability with strong jets. [ABSTRACT FROM AUTHOR]

OBJECTIVE: The aim of this study was to investigate whether microRNA-625-3p participated in the malignant progression of gastric cancer and inhibited GCa metastasis by regulating EZH2 (Enhancer of zeste homolog 2). PATIENTS AND METHODS: Quantitative Real Time-Polymerase Chain Reaction (qRT-PCR) was performed to examine the expression of microRNA- 625-3p in 36 pairs of GCa tissues and para-cancerous tissues. The interplay between microRNA-625-3p level and clinical indexes or prognosis of GCa patients was analyzed. MicroRNA- 625-3p mimics and inhibitors, as well as their negative controls, were transfected into GCa cell lines to establish microRNA-625-3p overexpression and down-regulation models in vitro, respectively. QRT-PCR was applied to further verify the transfection efficiency. Cell counting kit-8 (CCK-8), colony formation, and transwell assays were performed to analyze the impact of microRNA-625-3p on the proliferative and invasiveness abilities of GCa AGS and SGC-7901 cells. Finally, the regulatory mechanism of microRNA-625-3p on the downstream gene EZH2 was explored by cell reverse experiment. RESULTS: QRT-PCR results revealed that microRNA- 625-3p expression level in GCa tissues was remarkably lower than that of adjacent tissues, and the difference was statistically significant (p<0.05). Compared with patients with high expression of microRNA-625-3p, the incidence of lymph node or distant metastasis was significantly higher in patients with low expression of miR-625- 3p, whereas the overall survival rate was lower (p<0.05). Compared with GCa cells in NC inhibitor group, the proliferative ability and invasiveness of cells in microRNA-625-3p inhibitor group were remarkably promoted (p<0.05). However, the opposite results were observed in microRNA-625-3p mimics group. Our findings further demonstrated that the expression of EZH2 increased remarkably in GCa cell lines and tissues (p<0.05). Meanwhile, its expression level was negatively correlated with microRNA-625-3p level. Cell reverse experiment showed that EZH2 could offset the influence of microRNA-625-3p on the proliferation and metastasis GCa cells, thereby affecting the malignant progression of GCa. CONCLUSIONS: MicroRNA-625-3p was remarkably correlated with lymph node or distant metastasis and poor prognosis of GCa patients. In addition, microRNA-625-3p might inhibit the malignant progression of GCa via modulating EZH2. [ABSTRACT FROM AUTHOR]

OBJECTIVE: Pancreatic cancer (PC) possesses a very poor prognosis, and its pathogenesis is not fully understood. Evidence has suggested that microRNAs play important roles in cancer development and progression, the present study was designed to study the function of miR-1271 in PC. PATIENTS AND METHODS: PC tissues and adjacent normal tissues were collected from 17 patients. MiR-1271 and PDK1 expression were quantified by quantitative reverse-transcriptional polymerase chain reaction (RT-PCR). AKT/MTOR signaling activity and PDK1 protein expression were determined by Western blot. Cell viability and apoptosis were assessed by MTT assay and enzyme-linked immunosorbent assay (ELISA). Luciferase assay was used to verify whether miR-1271 directly targets PDK1. RESULTS: MiR-1271 was significantly down-regulated in PC tissues compared with that in the paired normal adjacent tissue, and its expression was up-regulated dose-dependently upon cisplatin treatment in PC cells. Overexpression of miR- 1271 in these cells produced a pro-apoptotic effect, similar to what caused by cisplatin treatment. Moreover, overexpression of miR-1271 inhibited AKT/MTOR signaling, which was due to the targeting relationship between miR-1271 and PDK1. Finally, knockdown of PDK1 exerted a similar effect on apoptosis to that of miR-1271 overexpression. CONCLUSIONS: MiR-1271 is a potent tumor suppressor in PC, its pro-apoptotic function was partially mediated by reduced AKT/MTOR signaling. Targeting miR-1271 may represent an effective strategy for PC treatment. [ABSTRACT FROM AUTHOR]

The applicability of six fine-resolution precipitation products, including precipitation radar, infrared, microwave and gauge-based products using different precipitation computation recipes, is comprehensively evaluated using statistical and hydrological methods in a usually-neglected area (northeastern China), and a framework quantifying uncertainty contributions of precipitation products, hydrological models and their interactions to uncertainties in ensemble discharges is proposed. The investigated precipitation products include TRMM3B42, TRMM3B42RT, GLDAS/Noah, APHRODITE, PERSIANN and GSMAP-MVK+. Two hydrological models of different complexities, i.e., a water and energy budget-based distributed hydrological model and a physicallybased semi-distributed hydrological model, are employed to investigate the influence of hydrological models on simulated discharges. Results show APHRODITE has high accuracy at a monthly scale compared with other products, and the cloud motion vectors used by GSMAP-MVK+ show huge advantage. These findings could be very use ful for validation, refinement and future development of satellite-based products (e.g., NASA Global Precipitation Measurement). Although significant uncertainty exists in heavy precipitation, hydrological models contribute most of the uncertainty in extreme discharges. Interactions between precipitation products and hydrological models contribute significantly to uncertainty in discharge simulations and a better precipitation product does not guarantee a better discharge simulation because of interactions. It is also found that a good discharge simulation depends on a good coalition of a hydrological model and a precipitation product, suggesting that, although the satellite-based precipitation products are not as accurate as the gauge-based product, they could have better performance in discharge simulations when appropriately combined with hydro logical models. This information is revealed for the first time and very beneficial for precipitation product applications. [ABSTRACT FROM AUTHOR]

Atmospheric submicron particulate matter (PM1) is one of the most significant pollution components in China. Despite its current popularity in the studies of aerosol chemistry, the characteristics, sources and evolution of atmospheric PM1 species in the East China are still poorly understood. Particular situations are the two harvest seasons, namely summer wheat harvest and autumn rice harvest. An Aerodyne Aerosol Chemical Speciation Monitor (ACSM) was deployed for online continuous monitoring of PM1 components during summer and autumn harvest seasons in urban Nanjing situated in the Yangtze River Delta (YRD) region of China. Results show that organic aerosol (OA) was the most abundant PM1 component, accounting for 39% and 41% of the total mass during the summer and autumn harvest periods, respectively. Positive matrix factorization (PMF) analysis resolved three OA components, i.e., hydrocarbon-like OA (HOA), biomass burning OA (BBOA), and oxygenated OA (OOA), which on average accounted for 19% (30 %), 17% (18 %), and 64% (52 %) of the total OA mass concentrations during the summer (autumn) harvest respectively. The BBOA mass fraction increases with an increase of high PM1 mass loadings (PM1 > 100 µgm-3), implying that BBOA plays a dominate role in high PM pollution during the harvest seasons. The mass concentrations of BBOA correlate well with the mass concentration of water-soluble potassium (K+), indicating that the atmospheric K+ is a good tracer for both wheat and rice straw burning during the harvest seasons. The BBOA mass concentrations for the summer and autumn harvest can be estimated as BBOA = 36.7 x (m/z 60-0.26% x OA) and = 41.4 x (m/z 60-0.26% x OA), respectively, m/z 60 as an identified marker for levoglucosan-like species. The OA mass decreases with the aging of BB plumes, implying that the fresh BB plumes contribute to atmospheric OA burden significantly. Combination of back-trajectory analysis with local wind indicates that the heavy pollution during the harvest seasons in the YRD region was found to be associated with transport processes and local source emissions. [ABSTRACT FROM AUTHOR]

Two mathematical models (i.e., perturbation and energy balance equations) are established to study the nonlinear stability of two-phase flow in the Blasius boundary layer based on the weakly nonlinear theory. The derived equations are discretized using the finite difference method. The results show that the averaged Reynolds stress is the fundamental consequence of the nonlinearity, and has a substantial effect on the mean flow. The distortion of the mean flow caused by the Reynolds stress modifies the rate of energy transfer from the mean flow to disturbance. The existence of particles alleviates the distortedness. The minimum critical Reynolds number is close to but less than the calculated value from the linear stability equation. The addition of fine and coarse particles to the Blasius boundary layer has destabilizing and stabilizing effects, respectively. The nonlinear interaction between mean flow and disturbance reduces the growth rate of the disturbance, while the nonlinear interaction between particle phase and gas phase increases the growth rate of the disturbance. [ABSTRACT FROM AUTHOR]