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In this paper, the integral event-triggered time-varying formation tracking (TVFT) problem is investigated for unmanned aerial vehicle (UAV) swarm systems with switching directed topologies. An improved integral event-triggered mechanism (ETM) is introduced into the TVFT control protocol, which can further reduce communication frequency and resource consumption compared with traditional static ETM. The switching topology is considered to improve the reliability of the communication network. Different from traditional TVFT, the addition of the switching signal and the ETM brings challenges to the system analysis and design. To this end, the control protocol of TVFT, the admissible edge-dependent average dwell time switching signal and the ETM are co-designed, the global exponential stability criterion is further deduced. The simulation verifies the effectiveness and merits of the design scheme. [ABSTRACT FROM AUTHOR]

A new enantioselective open-tubular capillary electrochromatography (OT-CEC) was developed employing β-cyclodextrin covalent organic frameworks (β-CD COFs) conjugated gold-poly glycidyl methacrylate nanoparticles (Au-PGMA NPs) as a stationary phase. The resulting coating layer on the inner wall of the fabricated capillary column was characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), energy dispersive spectroscopy (EDS), and electroosmotic flow (EOF) experiments. The performance of the fabricated capillary column was evaluated by CEC using enantiomers of seven model analytes, including two proton pump inhibitors (PPIs, omeprazole and tenatoprazole), three amino acids (AAs, tyrosine, phenylalanine, and tryptophan), and two fluoroquinolones (FQs, gatifloxacin and sparfloxacin). The influences of coating time, buffer concentration, buffer pH, and applied voltage on enantioseparation were investigated to obtain satisfactory enantioselectivity. In the optimum conditions, the enantiomers of seven analytes were fully resolved within 10 min with high resolutions of 3.03 to 5.25. The inter- to intra-day and column-to-column repeatabilities of the fabricated capillary column were lower than 4.26% RSD. Furthermore, molecular docking studies were performed based on the chiral fabricated column and as ligand isomers of analytes using Auto Dock Tools. The binding energies and interactions acquired from docking results of analytes supported the experimental data. [ABSTRACT FROM AUTHOR]

The conversion mode control scheme for tilt-rotor aircraft is provided with a switched Takagi-Sugeno (T-S) fuzzy modeling method and an adaptive anti-disturbance reference model tracking technique. In order to describe the dynamic features of the tilting process, a switched T-S fuzzy model is constructed with respect to the inclination angle. Compared to the linearized model, the initial nonlinear characteristics of the mathematical description are retained by the fuzzy modeling process, including the nonlinear disturbance input. Hence, an adaptive controller is designed to eliminate the adverse impact of composite disturbances caused by the rotor effect and the natural wind, which guarantees an L 2 - L ∞ performance of the corresponding error system. Furthermore, a simulation result with respect to the XV-15 tilt-rotor aircraft is given to verify the effectiveness of the proposed control scheme. [ABSTRACT FROM AUTHOR]

The histamine H4 receptor (H4R) plays key role in immune cell function and is a highly valued target for treating allergic and inflammatory diseases. However, structural information of H4R remains elusive. Here, we report four cryo-EM structures of H4R/Gi complexes, with either histamine or synthetic agonists clobenpropit, VUF6884 and clozapine bound. Combined with mutagenesis, ligand binding and functional assays, the structural data reveal a distinct ligand binding mode where D943.32 and a π-π network determine the orientation of the positively charged group of ligands, while E1825.46, located at the opposite end of the ligand binding pocket, plays a key role in regulating receptor activity. The structural insight into H4R ligand binding allows us to identify mutants at E1825.46 for which the agonist clobenpropit acts as an inverse agonist and to correctly predict inverse agonism of a closely related analog with nanomolar potency. Together with the findings regarding receptor activation and Gi engagement, we establish a framework for understanding H4R signaling and provide a rational basis for designing novel antihistamines targeting H4R.The histamine H4 receptor (H4R) plays key roles in immune cell function. Here, the authors report structures of H4R-Gi complex with various ligands bound, revealing distinct ligand binding modes and a basis for rational design of novel antihistamines targeting H4R. [ABSTRACT FROM AUTHOR]

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Perfluoroalkyl substances (PFASs) constitute an environmentally persistent and widespread class of anthropogenic chemicals that have been used in industrial and commercial applications in the USA and around the world. Animal studies suggested its toxic impact on lung development, but the adverse effect of PFAS exposure on childhood pulmonary function has not been clearly determined. We investigated the potential cross-sectional association of environmental PFAS exposures with pulmonary function in 765 adolescents aged 12–19 years from the US National Health and Nutrition Examination Survey (NHANES) 2007–2012. Exposure to PFASs was estimated by measuring serum concentrations, and pulmonary function was assessed by spirometry. Linear regression and weighted quantile sum (WQS) regression were performed to estimate the associations of individual chemicals and chemical mixtures with pulmonary function. Median concentrations of PFOA, PFOS, PFNA, and PFHxS (detection frequencies > 90%) were 2.70, 6.40, 0.98, and 1.51 ng/mL, respectively. No associations were found between the four individual congeners and Σ4PFASs and the pulmonary function measures in total adolescents. Sensitive analyses were further conducted stratified by age (12–15 and 16–19 years) and sex (boys and girls). In adolescents aged 12–15 years, PFNA was negatively associated with FEV1:FVC (p-trend = 0.007) and FEF25–75% (p-trend = 0.03) among girls, while PFNA was positively associated with FEV1: FVC (p-trend = 0.018) among boys. No associations were found among adolescents aged 16–19 years, either boys or girls. The aforementioned associations were confirmed when further applying WQS models, and PFNA was identified to be the most heavily weighing chemical. Our results suggested that environmental exposure to PFNA may affect pulmonary function among adolescents aged 12–15 years. Given the cross-sectional analysis and less consistent results, further replications of the association in large prospective cohort studies are warranted. [ABSTRACT FROM AUTHOR]

To effectively reduce the filtration rate of water-based fracturing fluid and promote the pressure holding effect of fracturing fluid in underground unconventional reservoirs, an efficient and clean organic-boron cross-linker was synthesized with boric acid and low alcohols. The results obtained that the synthesized organoboron cross-linker exhibits better fluid loss performance to water-based fracturing fluid than the commercially available cross-linker. This organoboron cross-linker allowed decreasing filtration coefficient more than 0.74 × 10–2 m3·min1/2 as a result of the network structure formed by the organoboron cross-linker and guar gum molecule. However, commercially available cross-linker exhibits a relatively large filtered mass of water more than 1.33 × 10–2 m3·min1/2 at the same condition. Meanwhile, the cross-linked guar gum fracturing fluid can significantly improve the fluid loss property with the increase of cross-linker content and pressure, and an increased fluid filtration gradually was revealed with increasing the reservoir temperature and current speed. Moreover, the damage of shale reservoir caused by the prepared boron cross-linker was only 11%, which was lower than 18% of the commercial boron cross-linker under the same conditions. [ABSTRACT FROM AUTHOR]

In this study, we have analyzed the impact of COVID-19 on natural gas supply reliability. Natural gas supply reliability is defined as the ability to satisfy the market demand and is determined by both supply-side and demand-side policy. To evaluate the gas supply reliability of the natural gas pipeline system, we have applied the method of gas supply capacity calculation based on the results of the previous gas supply reliability studies. The method combines the unsteady flow hydraulic analysis, simulation of the state transition process, and the forecasting analysis of the demand and consumption. The analysis presents a case study based on the gas pipeline system in China. The analysis results indicate that the COVID-19 consequences will cause a decrease in gas supply reliability. [ABSTRACT FROM AUTHOR]

Endometrial cancer is one of the most prevalent tumors of the female reproductive system causing serious health effects to women worldwide. Although numerous studies, including analysis of gene expression profile and cellular microenvironment have been reported in this field, pathogenesis of this disease remains unclear. In this study, we performed a system bioinformatics analysis of endometrial cancer using the Gene Expression Omnibus (GEO) datasets (GSE17025, GSE63678, and GSE115810) to identify the core genes. In addition, exosomes derived from endometrial cancer cells were also isolated and identified. First, we analyzed the differentially expressed genes (DEGs) between endometrial cancer tissues and normal tissues in clinic samples. We found that HAND2-AS1, PEG3, OGN, SFRP4, and OSR2 were co-expressed across all 3 datasets. Pathways analysis showed that several pathways associated with endometrial cancer, including "p53 signaling pathway", "Glutathione metabolism", "Cell cycle", and etc. Next, we selected DEGs with highly significant fold change and co-expressed across the 3 datasets and validated them in the TCGA database using Gene Expression Profiling Interactive Analysis (GEPIA). Finally, we performed a survival analysis and identified four genes (TOP2A, ASPM, EFEMP1, and FOXL2) that play key roles in endometrial cancer. We found up-regulation of TOP2A and ASPM in endometrial cancer tissues or cells, while EFEMP1 and FOXL2 were down-regulated. Furthermore, we isolated exosomes from the culturing supernatants of endometrial cancer cells (Ishikawa and HEC-1-A) and found that miR-133a, which regulates expression of FOXL2, were present in exosomes and that they could be delivered to normal endometrial cells. The common DEGs, pathways, and exosomal miRNAs identified in this study might play an important role in progression as well as diagnosis of endometrial cancer. In conclusion, our results provide insights into the pathogenesis and risk assessment of endometrial cancer. Even so, further studies are required to elucidate on the precise mechanism of action of these genes in endometrial cancer. [ABSTRACT FROM AUTHOR]

The MEN1 gene, a tumor suppressor gene that encodes the protein menin, is mutated at high frequencies in neuroendocrine (NE) tumors; however, the biological importance of this gene in NE-type lung cancer in vivo remains unclear. Here, we established an ATII-specific KrasG12D/+/Men1−/− driven genetically engineered mouse model and show that deficiency of menin results in the accumulation of DNA damage and antagonizes oncogenic Kras-induced senescence and the epithelial-to-mesenchymal transition during lung tumorigenesis. The loss of menin expression in certain human primary lung cancers correlates with elevated NE profiles and reduced overall survival. Loss ofMEN1 results in an inherited multiple endocrine neoplastic type 1 syndrome. Here, the authors generate an alveolar type II cell MEN1 knockout mouse model and show that on a Kras mutant background the mice develop lung tumors with features of neuroendocrine differentiation. [ABSTRACT FROM AUTHOR]

In this paper, Saint-Venant's principal has been introduced into energy decay inequality to compute parameters and prestress for eigenanalysis, under the assumption that the transverse force is equal to the reaction of elastic constraints. In addition, the main tasks that are accomplished in the article are proposed as novel approach dynamic stiffness method, to analyze free vibration of 1D cantilever structures, with random boundaries. The numerical simulation showed that the proposed process gives high degree of accuracy in the calculation of natural frequencies for 1D beams with arbitrary boundary conditions as soon as the structural model was established. Moreover, the proposed model is particularly useful when analyzing 1D structures with random boundary conditions since it matches encouragingly well with the corresponding MCS results. [ABSTRACT FROM AUTHOR]

Slug anti-gas channeling technology was studied in laboratory experiments to optimize the micro-expansion behavior of its material. The technology included sealing of an outer pipe, injection of cement slurry into the casing annulus, and activation and solidification of the cement slurry as a function of temperature and other external conditions. The technology could effectively seal an oil or gas well and solve the problem of wellhead pressure. [ABSTRACT FROM AUTHOR]

This work is concerned with H ∞ filter design with missing measurements for a class of two-dimensional (2-D) switched systems represented by Fornasini–Marchesini local state-space model. The switching signal of the switched filters involve time delays, which result in the asynchronism between the filter and the system switching. The issues of asymptotic mean-square stability and ℓ 2 -gain analysis for the 2-D switched systems are addressed firstly, based on which mode-dependent filters are designed with mode-dependent average dwell time scheme. Finally, two examples are given to demonstrate the validity of the proposed technique. [ABSTRACT FROM AUTHOR]

Carbon and their compounds were removed successfully through electron beam melting (EBM), so that those areas (contaminated with carbon) of ingot were recycled and reused. During EBM process, the numerical simulation results show that there is great temperature gradient existing in the melt. During EBM, the melt near copper crucible shows low temperature and bad fluidity. Carbon in silicon melt flows, precipitated and gathered in this area so that it is separated. The flow mechanism of SiC in silicon melt was investigated. After EBM, carbon enriches in the form of SiC at the bottom of the ingot but not in the center. This technology is applied on industrial scale EBM equipment. The results show that a majority of SiC was deposited in the bottom of the refining crucible and the carbon contaminations are not found in the most of the area of the solidified ingot in crucible. [ABSTRACT FROM AUTHOR]

Two 450 kg multicrystalline silicon ingots were obtained by mixing and melting high purity silicon and silicon from the edges and the bottom of the casted ingots together in a casting furnace. For one of the ingot, the silicon from casted ingots was refined in an electron beam melting furnace to remove oxygen. The oxygen content was reduced from 10 to less than 0.0517 ppmw when silicon was refined at 500 kW with removal efficiency up to 99.429% in the most areas. The life time of the ingot after oxygen removal was measured to be far better than another one, whereas in the central parts the value was almost 6.7 µs. The efficiencies of both solar cells were initially 17.55% but after 4 h decreased to 17.05% and 15.55%, respectively. The solar cell after oxygen removal shows a better performance in degradation. [ABSTRACT FROM AUTHOR]

Elastic wave propagation and attenuation in porous rock layers with oriented sets of fractures, especially in carbonate reservoirs, are anisotropic owing to fracture sealing, fracture size, fracture density, filling fluid, and fracture strike orientation. To address this problem, we adopt the Chapman effective medium model and carry out numerical experiments to assess the variation in P-wave velocity and attenuation, and the shear-wave splitting anisotropy with the frequency and azimuth of the incident wave. The results suggest that velocity, attenuation, and anisotropy vary as function of azimuth and frequency. The azimuths of the minimum attenuation and maximum P-wave velocity are nearly coincident with the average strike of the two sets of open fractures. P-wave velocity is greater in sealed fractures than open fractures, whereas the attenuation of energy and anisotropy is stronger in open fractures than sealed fractures. For fractures of different sizes, the maximum velocity together with the minimum attenuation correspond to the average orientation of the fracture sets. Small fractures affect the wave propagation less. Azimuth-dependent anisotropy is low and varies more than the other attributes. Fracture density strongly affects the P-wave velocity, attenuation, and shear-wave anisotropy. The attenuation is more sensitive to the variation of fracture size than that of velocity and anisotropy. In the seismic frequency band, the effect of oil and gas saturation on attenuation is very different from that for brine saturation and varies weakly over azimuth. It is demonstrated that for two sets of fractures with the same density, the fast shear-wave polarization angle is almost linearly related with the orientation of one of the fracture sets. [ABSTRACT FROM AUTHOR]

To evaluate the effects of two-dimensional (2D) programming on thermal decomposition of shape memory polymer (SMP)-based composites when exposed to fire, the block specimens of SMP-based composites were first prepared and programmed. Then the phase structure and thermal decomposition properties of SMP-based composites were characterized before and after the 2D programming. Also, the released volatile constitutes were identified, and the microscopic morphology of charring layer was observed, and thermal decomposition mechanism of SMP-based composites was discussed. Results indicated that SMP-based composites had two phases, and the crystalline segments were not found in both non-programmed and programmed samples. The 2D programming disorients the hard phase and soft phase in the SMP matrix. Additionally, the 2D programmed SMP-based composites showed lower thermal stability than the non-programmed sample. Further, the released volatile constitutes of non-programmed composites were consistent with those of the programmed sample. However, the programmed composites released more volatiles during its thermal decomposition. Finally, the charring layer of non-programmed SMP-based composites was more continuous and compacted than that of programmed sample, preventing the volatiles from releasing out of SMP, and increasing the resistance of SMP-based composites to high temperature. The 2D programming facilitated both chain scission and cross-linking reactions during the thermal decomposition of SMP-based composites. The former released heat and gaseous products to sustain burning and produced smokes, while the latter caused the aromatization and condensation to form combustion residues. [ABSTRACT FROM AUTHOR]

This research deals with the study of electron beam melting (EBM) methodology utilized in melting silicon material and subsequently discusses on the effect of oxygen level on electrical resistivity change after EBM process. The oxygen content was reduced from 6.177 to less than 0.0517 ppmw when refining time exceeded 10 min with removal efficiency of more than 99.08%. The average value of electrical resistivity of silicon before EBM processing was recorded to be 2.25 Ω cm but with the increase in melting time that was applied through EBM, the electrical resistivity was recorded to go high in the range of 4-13 Ω cm for different regions. The electrical resistivity values were greater in the top and the bottom regions, whereas lowest in the central region at all conditions of melting time. It is the result of the evaporation of oxygen during melting process and the segregation of metal impurities during solidification. [ABSTRACT FROM AUTHOR]

Tree bark was used as the passive air sampler to evaluate polychlorinated biphenyl (PCB) and polybrominated diphenyl ether (PBDE) pollution and possible sources in Southern Jiangsu. The concentrations of PCBs and ΣPBDEs were in the range of 0.58-5.19 ng/g dry weight (dw; mean 1.79 ng/g dw) and 17.9-243 pg/g dw (mean 74.7 pg/g dw), respectively. Tri-PCBs were the major PCB homologs, and technical PCB product Ar1242 was identified as the main source. BDE209 concentrations (4.29-456 ng/g dw) were relatively high, indicating that BDE209 pollution was serious in this region. The deca-BDE commercial mixture was the predominant commercial PBDE product used in this region. A good correlation was found between tree bark and polyurethane foam (PUF) disks in ΣPCB monitoring, suggesting that both of them respond well to the gas-phase PCB monitoring. [ABSTRACT FROM AUTHOR]

Surface soil samples were collected from urban agglomeration of the Yangtze River Delta (YRD), China in 2003 and 2012, respectively. Polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) were analyzed to determine if there were any changes in their levels and compositional profiles between the two sampling years. The concentrations of ΣPBDEs ranged from 0.553 to 13.0 μg kg(with the mean of 3.31 μg kg) in the 2003 samples and from 1.01 to 43.2 μg/kg (with the mean of 10.0 μg kg) in the 2012 samples. The concentrations of ΣPCBs ranged from 0.301 to 3.29 μg kg(with the mean of 1.01 μg kg) in the 2003 samples and from 0.205 to 3.96 μg/kg (with the mean of 0.991 μg kg) in the 2012 samples. The comparisons between the 2012 and 2003 data showed that PBDEs concentrations increased over the years, but PCB concentrations did not change much. BDE-209 was the major BDE congener in both the 2003 and 2012 samples, indicating that the dominant PBDE mixture production and usage in the YRD had been the commercial deca-BDE mixture. Investigation of the PBDE congener profiles indicated that there had been new input of octa-BDEs in this region in recent years. Little change was found for the pattern of PCBs congener profiles between 2 years' samples. As such, spatial distributions of PBDEs or PCBs in surface soil samples reflected a gradient (from high to low) from the central cities out to rural areas in both the 2003 and 2012 data. In addition, high concentrations of PBDEs were observed in the industrial and residential areas, whereas high concentrations of PCBs were only observed in the industrial areas. [ABSTRACT FROM AUTHOR]

Small amounts of multicrystalline silicon were melted in an electron beam furnace in different experimental conditions in order to investigate the oxygen evaporation behavior during the electron beam melting (EBM) process. The oxygen content level before and after EBM was determined by secondary ion mass spectroscopy. The oxygen content was reduced from 6.177 to 1.629 ppmw when silicon was melted completely at 15 kW with removal efficiency up to 73.6 %. After that, it decreased continually to <0.0517 ppmw when the refining time exceeded 600 s with a removal efficiency of more than 99.08 %. During the melting process, the evaporation rate of silicon is 1.10 × 10 kg/s. The loss of silicon could be reduced up to 1.7 % during oxygen removal process to a desirable figure, indicating EBM is an effective method to remove oxygen from silicon and decrease the loss of silicon. [ABSTRACT FROM AUTHOR]

Silicon is widely used as a raw material for production of solar cells. As a major impurity in silicon, phosphorus must be removed to 1 × 10 wt.%. In the present study, based on the distribution of phosphorus in a silicon ingot obtained by vacuum refining and directional solidification, the mechanism for removal of phosphorus from silicon is investigated. The results show that the distribution is controlled not only by segregation at the solid-liquid interface but also by evaporation at the gas-liquid interface, showing some deviation from Scheil's equation. A modified model which considers both segregation and evaporation is used to simulate the distribution, matching quite well with the experimental results. The temperature and solidification rate are two important parameters that affect the overall mass transfer coefficient and the effective segregation coefficient and thus the distribution of phosphorus. A high removal efficiency and a homogeneous distribution can be obtained by adjusting these two parameters. [ABSTRACT FROM AUTHOR]