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The propagation of the weak shock wave (WSW) to the tunnel exits and their radiation as micro-pressure waves (MPWs) may cause sonic booms or structural resonance of buildings, posing potential hazards to humans, animals, and buildings in the exit's environment. The characteristics of the WSW and sonic booms of a maglev train/tube coupling model were studied based on the two-dimensional axisymmetric unsteady Reynolds average Navier–Stokes turbulence model. In the later stage of a MPW, the formation mechanism, geometry, and kinematic characteristics of compressible vortex rings (CVRs) were systematically analyzed. The inertial effect causes the initial wavefront to gradually transition from a Gaussian-shape waveform to a triangular waveform during its propagation, eventually coalescing into a WSW. The overpressure, density jump, and shock Mach number at the WSW location all increase with the increasing train speed, while the WSW thickness decreases accordingly. The formation distance of the WSW is inversely proportional to the amplitude of the initial wavefront gradient, and the WSW directly causes the occurrence of the exit sonic boom. The MPW amplitude has significant directionality with a largest value in the axial direction. Within the speed range of 450–700 km/h, the sound pressure level of the MPW exceeds the hearing threshold and even reaches the feeling threshold. The evolution of CVRs includes primary CVR, secondary CVR, and Kelvin–Helmholtz vortices. Primary CVR has the greatest impact on the axial MPW among them. The occurrence of CVRs will cause a second small noise level other than the sonic boom. [ABSTRACT FROM AUTHOR]

The turbulence intensity and yaw angle of crosswinds exert a substantial impact on the aerodynamic characteristics of trains traveling in windy regions. It is urgent to study how the yaw angle and turbulence intensity of incoming flow jointly affect the aerodynamic characteristics of the train and the corresponding flow field under turbulent crosswind. A high-speed train scaled at a ratio of 1/8 of its actual size at different yaw angles was investigated. Three inflow conditions were adopted, including uniform inflow, Iu = 0.05 inflow, and Iu = 0.2 inflow (Iu is turbulence intensity). The turbulent inflow was generated by the synthetic eddy method. The instantaneous and time averaged characteristics of aerodynamic loads and pressure loads of the train were analyzed. The vortex structures, vorticity, swirling strength, mean velocity, reverse flow, and Reynolds stresses are analyzed to explore the flow pattern and flow evolution. The results found that the fluctuation of the aerodynamic loads, the average side fore, and the average rolling moment of the train are remarkably enhanced under turbulent inflow. These results stem from the alterations in the flow field around the train induced by turbulent inflow, consequently leading to variations in surface pressure on the train. As the turbulence intensity of the inflow increases, the stability of the vortex structures decreases, and the position of the large-scale vortex structure has been changed. Moreover, the yaw angle (β) exerts a more significant influence on the vortex structure's flow pattern on the leeward side compared to the inflow turbulence intensity. [ABSTRACT FROM AUTHOR]

With the increase in high-speed train (HST) operation speed, the light-weight design of the train body and component structure is pursued to reduce energy consumption during operation, but this seriously deteriorates the aerodynamic performance of the light-weight structure outside the train body under the effect of strong unsteady airflow, and the more obvious case is the frequently occurring problem of vibration, large deformation, and damage to the rubber exterior windshield at the connection position of HST carriages. We investigate the fluid–structure coupling mechanism of the interaction between the rubber external windshield and aerodynamic force, and compare the dynamic characteristics of windshield structure under different design parameters. A numerical simulation of three rubber outer windshield structure parameters (sidewall distance of U-shaped capsule, sidewall thickness, sidewall inclination angle) is carried out using FSI simulation of the two-way coupling method. The aerodynamic load, airflow dynamics around the windshield, and the nonlinear vibration and deformation form of the windshield is analyzed in detail. The results show that the aerodynamic response of the HST rubber external windshield analyzed by the FSI method is in good agreement with the full-scale test results. Additionally, the stiffness of the windshield can be improved by increasing the thickness of the windshield sidewall. When the distance between the sidewall of the windshield is increased, an insufficient thickness at the top of the arc causes a large local deformation at the top of the arc of the windshield. The method established and relevant research results can provide good support for the aerodynamic stability evaluation of HST windshields. [ABSTRACT FROM AUTHOR]

Turbulent incoming flow conditions are closely matched to the crosswinds experienced by trains in windy areas. Therefore, it is important to investigate how the turbulent inflow affects the flow dynamics around a train. The aerodynamic characteristics of a 1:8-scaled high-speed train at a 90° yaw angle were studied based on the improved delayed detached eddy simulation (IDDES) turbulence model. Four incoming flow conditions were set using a synthetic eddy method (SEM) turbulent generator, including uniform, Lu = 0.5H, Lu = 1H, and Lu = 2H inflow (Lu is turbulence integral length scale and H is reference height). The aerodynamic loads, surface pressure, mean vorticity, vortex structure, velocity deficit, turbulence characteristics, Reynold stresses, turbulence production term, and anisotropy of turbulence were thoroughly analyzed. Turbulent inflow and increasing inflow Lu increased the standard deviation of the aerodynamic loads on the train. A crisis of inflow Lu appeared around 0.5H, meaning the rolling moment and overturning moment were largest under this crisis condition. Turbulent inflow caused vortices on the train's leeward side to come closer to the train, increasing the vorticity thickness and shortening the back flow region. The Reynolds stresses on the train's leeward side under turbulent inflow conditions were strengthened. The spectrum-proper orthogonal decomposition method was used to analyze the dominant mode within the train's leeward region and the corresponding energy distribution in the frequency domain. The aerodynamic admittance function was used to investigate the frequency characteristics of the aerodynamic loads on the train. [ABSTRACT FROM AUTHOR]

By using three different head types (5 m, 7.5 m and 10 m nose lengths), the CRH3 (China Railway High-speed 3) flow field structure at 15° yaw was studied through wind tunnel experiments and numerical simulations. The modifications of the aerodynamic coefficients were studied using the Improved Delayed Separation Eddy Simulation (IDDES) method. The results show that the longer the nose length of the tail car, the more it is affected by crosswind. However, the increase in turbulence mitigates the risk of overturning the tail car as the pressure distribution between the train side surface and the underbody becomes more disturbed. The nose length of the head car can affect the position and length of the longitudinal vortex core on the leeward side, thus affecting the lift and side force of each section of the train. The location of the time-averaged vortex core for a 15° crosswind is approximately 0.67H~0.7H high from the ground and 0.65H~0.67H wide from the center of the train. The main frequency of the leeward vortex ranges from 0.1 to 0.3. The transient vibration amplitude at the position of the vortex core is the largest, and the main frequency of vibration is 0.18. The tail car nose length should be properly lengthened since increasing the length of the tail car reduces the negative pressure on the surface of the tail car, thus reducing drag and side force. However, the excessive length of the tail car nose increases the risk of overturning under crosswind. [ABSTRACT FROM AUTHOR]

The external windshield is a key component in high-speed trains for drag reduction. However, the installation gap between external windshields, which is intended for improving curve-passing ability, could lead to strong aerodynamic instability in train-end area and therefore significant operating risk for train. This study aims to advance this field based on detailed numerical simulation, investigating the related flow features in this area, particularly from a time-dependent perspective. Flow field around external windshields with different installation gaps (10, 20 and 30 mm) is resolved based on Improved Delayed Detached Eddy Simulation (IDDES). The aerodynamic forces on different windshield components, turbulent flow fields around the train-end area, and corresponding low-dimensional modes are analyzed. The results show that the difference in the external windshield gap can significantly affect the related aerodynamic forces, with the 20 mm case having the highest time-averaged values. The aerodynamic spectrum shows primary, secondary and tertiary peak frequencies with a relatively high power spectral density (PSD). Decreasing the gap distance generally increases the overall PSD in the Strouhal number ranges considered, particularly for the secondary and tertiary peaks. The load forms and their energy distributions under different external windshield gaps are obtained through the proper orthogonal decomposition analysis. [ABSTRACT FROM AUTHOR]

Coherent structures in surrounding flows around ground vehicles play an important role in characterizing their aerodynamic features. However, due to restrictions of traditional reduced-order models, extracting physically meaningful coherent structures from turbulent flows with massive separation still remains a challenging issue. The spectral proper orthogonal decomposition (SPOD), which extracts modes optimally representing the space-time flow statistics, enables the feasibility of further modeling and control of vehicle aerodynamic features. This study intends to investigate the influence of spectral estimation parameters on SPOD results, so as to serve as fundamentals for future works into this topic. The time-resolved pressure field obtained from a large-eddy simulation considering a generic high-speed train is used as the snapshot database. Spectral estimation parameters including block number, frequency resolution, and cutoff frequency are, respectively, discussed to quantify their impacts on both SPOD spectra and modes. The results reveal that, with the increasing of block number, higher reliability and accuracy of SPOD prediction can be achieved, with the block number of 20–30 that leads both requirements of efficiency and precision. The frequency axis with finer resolution reproduces more detailed spectral information, with the eigenvalue distribution and spatial distribution of mode energy under acceptable accuracy when dimensionless frequency resolution reaches 0.025. Moreover, the reducing of cutoff frequency results in increasing unresolved energy content, which will be distributed mostly near the corresponding cutoff frequency, and more minor scaled spatial structures in SPOD modes. The findings and approaches could also work as references for wider application field of SPOD approach. [ABSTRACT FROM AUTHOR]

Based on the Kachanov damage theory and elastic wave theory, considering the long-term creep damage from time dimension and instantaneous disturbance damage from space dimension, we presented a 3D damage creep model and converted it to difference expressions in order to write into the finite difference software FLAC3D. Then, according to the results of creep tests, we conducted parameter inversion of our damage creep model with the help of the particle swarm optimization (PSO) method. Finally, the damage creep model was applied in a railway tunnel project in Yunnan to simulate the tunnel deformation. Compared with the Burgers model and the model considering only creep damage, our model which considers both creep damage and disturbance damage yielded more reasonable results. [ABSTRACT FROM AUTHOR]

Triclosan (TCS) is a broad-spectrum antimicrobial agent that is broadly used in personal care products. It has been shown to cause the contamination of a variety of aquatic environments. Since algae has been the primary producers of aquatic ecosystems, understanding the toxicological mechanisms and the metabolic fate of TCS is vital for assessing its risk in an aquatic environment. In our study, 0.5–4 mg L−1 TCS treatments for 72 h in a culture of Chlamydomonas reinhardtii (C. reinhardtii) showed progressive inhibition of cell growth and reduced the chlorophyll content. The EC50 value of C. reinhardtii after 72 h was 1.637 mg L−1, which showed its higher level of resistance to TCS in comparison with other algal species. The exposure to TCS led to oxidative injuries of algae in relation to the increment of malonaldehyde content, cell membrane permeability, and H2O2 levels. Furthermore, the oxidative stress from TCS stimulated a series of antioxidant enzyme activities and their gene expressions. Simultaneously, the accumulated TCS in C. reinhardtii arouses the detoxification/degradation-related enzymes and related gene transcriptions. In the medium, approximately 82% of TCS was removed by C. reinhardtii. Importantly, eight TCS metabolites were identified by ultra-performance liquid chromatography-high-resolution mass spectrometry and their relative abundances were measured in a time-course experiment. Six of these metabolites are reported here for the first time. The metabolic pathways of triclosan via C. reinhardtii including reductive dechlorination, hydroxylation, sulfhydrylation, and binding with thiol/cysteine/GSH/glycosyl were manifested to broaden our understanding of the environmental fate of TCS. [ABSTRACT FROM AUTHOR]

Abstract A novel magnetic MIPs (DUMIPs) was prepared by surface molecular imprinting method using superparamagnetic core-shell nanoparticle (Fe 3 O 4 @SiO 2) as the sacrificial support matrix, herbicide diuron as template, α-methacrylic acid as the functional monomer, trimethylolpropane trimethacrylate as the crosslinker, azobisisobutyronitrile as the initiator, and acetonitrile as the porogen. Highly cross-linked porous surface and excellent magnetic property were characterized by Fourier-transform infrared spectroscopy, transmission electron microscopy, and vibrating sample magnetometer, respectively. The adsorption capacity of DUMIPs was 8.1 mg g−1, 2.6-fold over its corresponding non-imprinted polymers (DUNIPs). The adsorption in DUMIPs was considered as multilayer adsorption and posed high affinity to diuron, due to the better fitting to Freundilich isotherm. Competitive recognition study demonstrated DUMIPs had highly selective binding diuron. DUMIPs, as an influential sorbent has been used for selective extraction of diuron from environmental samples (paddy field water, paddy soil and grain seedlings) and the elution was determined by high efficiency liquid chromatography (HPLC). In this analytical method, various factors affecting the extraction efficiency such as pH, sorbent dosage, utilization efficiency and volumes of eluent were simultaneously investigated. Under the optimal conditions, the linearity of the method obtained is in the range of 0.02–10.0 mg L−1. The limit of detection is 0.012 mg L−1. In four spiked levels (0.04, 0.2, 1.0, and 4.0 mg kg−1), the recoveries of diuron in real samples are in the range of 83.56%–116.10% with relative standard deviations in the range of 1.21–6.81%. Importantly, compared to C 18 -SPE column, the MMIPs exhibited convenient separation by external magnetic field, strong clean-up capacity, and selective enrichment for diuron. Thus, the DUMIPs-based method is great potential for efficient sample preparation in the determination of trace amounts of diuron residues in complex matrices. Graphical abstract Image 1 Highlights • Magnetic separation and surface imprinting were reasonably combined for smart material preparation. • SiO 2 -coated Fe 3 O 4 effectively prevent the agglomerate of magnetic nanoparticles. • The DUMIPs exhibited magnetic properties with specific recognition, high binding capacity, and fast binding kinetics. • The DUMIPs were feasible materials for selective enrichment and efficient separation of diuron from complicated matrices. [ABSTRACT FROM AUTHOR]

A series of novel 1,4-dihydro-2,6- dimethyl-3,5-pyridinedicarboxamides were synthesized and characterized by infrared absorption spectrum (IR), proton nuclear magnetic resonance (1H NMR), elemental analysis, ultraviolet spectrum (UV), and fluorescence techniques, together with X-ray single crystal diffraction. The results of density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations provided a reasonable explanation on the molecular structures, the molecular frontier orbital, and the spectra of electronic absorption and emission. The present work will be helpful to systematically understanding of the structures and the optical properties of 1,4-dihydropyridines for studying the structure-activity relationship and to develop new drugs and their analytical methods. [ABSTRACT FROM AUTHOR]

Triclosan (TCS) is a kind of chronic toxicity to aquatic organisms. Due to its highly effective antimicrobial, TCS has been widely applied in personal−care products, which naturally poses a potential risk to the ecological system and human health since its release into water−ecological environment. Therefore, it urgently demands a selective, easily separated, recyclable, and low−cost adsorbent to remove the residues of TCS from aquatic environments. In this study, a novel magnetic molecularly imprinted nano−polymers (TMIPs) were prepared for selective adsorption and convenient collection of TCS in aquatic samples, based on a core−shell technique using TCS as template molecule and SiO 2 −coated Fe 3 O 4 nanoparticles as the support substrate. The functional groups, particle size, morphology and magnetic property of TMIPs were characterized by Fourier−transform infrared spectroscopy, scanning electron microscope, transmission electron microscopy and vibrating sample magnetometer, respectively. The obtained TMIPs possessed excellent adsorption capacity (Q e = 53.12 mg g−1), speedy adsorption equilibrium time (2 min) and high selectivity (k' = 6.321) for TCS. Moreover, the pH−tolerance and stability tests manifested that the adsorption capacity of TMIPs for TCS was acid−resistance and could retain 94.2% of the maximum Q e after 5 times removal−regeneration cycles. The feature of magnetically susceptibility can simplify the procedures of sample handling in TCS determination, because the TMIPs of TCS are easy to be recycled from aquatic samples. As an application demonstration, the toxicity test in microalgae confirmed that a tiny amount of TMIPs could significantly eliminate the toxic effect of TCS on Chlamydomonas reinhardtii via the efficient binding with TCS. Image 1 • A kind of nano-polymers with magnetic property and excellent adsorption were prepared by core-shell technique. • The molecularly imprinted nano-materials (TMIPs) have specific binding with triclosan. • High recoveries in spiked aquatic samples proved that the TMIPs were feasible sample handling nanomaterials for rapid enrichment of triclosan. • TMIPs as magnetically recyclable sorbents were successfully applied in the efficient removal of triclosan from aquatic environments. [ABSTRACT FROM AUTHOR]

The title compound, C(20)H(17)N(3)O(2)S(2), was synthesized by the reaction of 2-(1,5-diphenyl-1H-pyrazol-3-yl-oxy)acetic acid and thia-zolidine-2-thione. The C-linked benzene ring, N-linked benzene ring and thia-zolidine-2-thione ring are twisted 31.33 (2), 62.87 (1) and 82.71 (2)°, respectively, from the plane of the bridging 1H-pyrazole ring. The phenyl rings are oriented at a dihedral angle of 72.16 (2)°.