Search Results (44)

A multidisciplinary investigation was conducted in southwestern Sicily, near the seismically active Belice Valley, based on the analysis of morphostructural features. These were observed as open fractures between 2014 and 2017; they were subsequently filled anthropogenically and then reactivated during a seismic swarm in 2019. We generated a seismic event distribution map to analyze the location, magnitude, and depth of earthquakes. This analysis, combined with multitemporal satellite imagery, allowed us to investigate the spatial and temporal relationship between seismic activity and fracture evolution. To investigate the spatial variation in thickness of the superficial cover and to assess the depth to the underlying bedrock or stiffer substratum, 45 Horizontal-to-Vertical Spectral Ratio (HVSR) ambient noise measurements were conducted. This method, which analyzes the resonance frequency of the ground, produced maps of the amplitude, frequency, and vulnerability index of the ground (K_g). By inverting the HVSR curves, constrained by Multichannel Analysis of Surface Waves (MASW) results, a subsurface model was created aimed at supporting the structural interpretation by highlighting variations in sediment thickness potentially associated with fault-controlled subsidence or deformation zones. The surface investigation revealed depressed elliptical deformation zones, where mainly sands outcrop. Grain-size and morphoscopic analyses of sediment samples helped understand the processes generating these shapes and predict future surface deformation. These elliptical shapes recall the liquefaction process. To investigate the potential presence of subsurface fluids that could have contributed to this process, Electrical Resistivity Tomography (ERT) was performed. The combination of the maps revealed a correlation between seismic activity and surface deformation, and the fractures observed were interpreted as inherited tectonic and/or geomorphological structures. Full article

Acoustic metamaterials and phononic crystals are progressively consolidating as an important technology that is expected to significantly impact the science and industry of acoustics in the coming years. In this work, the impact of unit cell multiplicity on the spectral features of the acoustic response of phononic crystals is systematically studied using the recently demonstrated laser-plasma sound source characterization method. Specifically, by exploiting the advantages of this method, the impact of the number of repeated unit cells on the depth of the phononic band gaps and the passband spectral features across the entire audible range is demonstrated. These experimental findings are supported by specially developed computational simulations accounting for the precise structural characteristics of the studied phononic crystals and are analysed to provide a phenomenological understanding of the underlying physical mechanism. It is shown that by increasing the unit cell multiplicity, the bandgaps deepen and the number of resonant peaks in the crystal transmission zones increases. The resonant mode shapes are computationally investigated and interpreted in terms of spherical harmonics. This study highlights the tunability and design flexibility of acoustic components using phononic crystals, opening new paths towards applications in the fields of sound control and noise insulation. Full article

We have compared the biomechanical properties of human and porcine corneas using vibrational optical coherence tomography (VOCT). The elastic modulus of the cornea has been previously reported in the literature to vary from about several kPa to more than several GPa based on the results of different techniques. In addition, the formation of corneal cones near the central cornea in keratoconus has been observed in the clinic. Measurements of the resonant frequency and morphology of human and porcine corneas were used to evaluate the role of the limbus in corneal stabilization, the effect of Bowman’s layer, and the effect of collagen content on the low-strain corneal biomechanics. The results of these studies indicate that limbus stability plays an important anatomic role in preventing folding, corneal slippage, and cone formation. Machine learning studies of both human and porcine corneas indicate that Bowman’s membrane, like that of the collagen fibrils found in the anterior corneal stroma, contributes to the 110–120 Hz resonant frequency peak. Finite element and SOLIDWORKS models of normal and keratoconus corneas suggest that the deformation of the cornea is the highest at the central zone and is higher in keratoconus corneas compared to normal controls. VOCT results suggest that although collagen fibril slippage occurs first at the limbus, cone formation in keratoconus occurs centrally/paracentrally, where stress concentration and deformation due to intraocular forces are the highest. Cone formation occurs at the points of maximum curvature. Results of these studies indicate the elastic modulus of cornea fibrillar collagen dictates the corneal elastic modulus at low strains. These results suggest that tension in the cornea at the limbus results in deformation into the low modulus region of the J-shaped stress–strain curve, resulting in an in vivo strain of less than about 10%. We propose that tension in the cornea provides a baseline force that regulates corneal epithelial regeneration as well as corneal lamellae composition and matrix turnover. Full article

Offshore wind is a promising renewable energy generation technology and is arousing great attention in regards to pursuing carbon neutrality targets. Accurately simulating offshore wind generation can help to better optimize its operation and planning. It is also a concern that mechanical resonance is a threat to the wind turbines’ lifespan. In this paper, the time-series simulation of offshore wind generation with consideration of resonance zone (RZ) control is investigated. The output model for multiple wind farms with different spatial correlations is proposed. Additionally, the capacity value (CV) of the joint wind farms is also evaluated through a reliability-based model. The case study illustrates the offshore wind power output simulation and CV results under different farm correlation scenarios and RZ control strategies. It is shown that strong spatial correlation brings great synchronicity in wind farms’ output and results in a lower CV. The RZ control in wind simulation is validated and proven to have a marginal impact on the total output when multiple wind farms are evaluated together. Full article

Trialeurodes vaporariorum Westwood poses a significant threat to vegetable and ornamental crops in temperate zones, resulting in notable reductions in yield and substantial economic burdens. In order to find compounds with high insecticidal activity against T. vaporariorum, five compounds were isolated and identified from the crude extract of Streptomyces sp. SA61. These include three new polyketides, named strekingmycins F–H (1–3); one new diterpenoid, named phenalinolactone CD8 (4); and one known compound, strekingmycin A (5). Their structures were analyzed using high-resolution electrospray ionization mass spectrometry and one-dimensional and two-dimensional nuclear magnetic resonance spectroscopy data and by comparing them with previously reported data. The insecticidal activities of compounds 1–5 against T. vaporariorum were evaluated. Among them, compound 5 exhibited the highest insecticidal activity, with an LC₅₀ of 6.949 mg/L against T. vaporariorum at 72 h using the leaf-dip method. Lower insecticidal activities were found in compounds 1–4, with LC₅₀ values of 22.817, 19.150, 16.981 and 41.501 mg/L, respectively. These data indicate that strekingmycin could be a potential candidate for a novel insecticide to control T. vaporariorum. Full article

Helium is an irreplaceable ore resource for many applications, such as nuclear magnetic resonance, aviation, semiconductors, and nuclear energy. Extracting helium in a free state from natural gas is currently the only economical approach at the industrial level. In this study, we compiled geochemical data of 719 natural gas samples from 36 oil and gas fields in the Tarim basin that include experimental results and previously reported data. Helium is of primarily crustal origin in the Tarim Basin according to helium isotope characteristics (not exceeding 0.1 Ra), except in the Ake gas field that has not more than 7% of mantle helium. Helium concentrations in diverse tectonic units vary considerably. Oil-type gas, on the whole, has a higher helium concentration relative to coal-type gas. Abundant helium flux, a favorable fault system between the source-reservoir system, no strong charging of gaseous hydrocarbons, and the good sealing capacity are important factors that control the formation of helium-rich gas fields. Considering both the helium concentration and natural gas reserves, helium-rich gas fields located in the Southwest Depression and Tabei Uplift can be regarded as the major favorable zones of further deployment for helium extraction. Full article

To enhance protection against corrosion and ice on iron metal material in frigid zones, an organic silicone resin coating was prepared using four monomers. Its structure and performance was analyzed via infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), and thermal analysis (TG). Corrosion resistance of coating was tested by saltwater resistance and salt spray resistance and assessed using an electrochemical workstation, alongside anti-icing tests. The results showed that the organic silicone resin was successfully synthesized. The coatings could delay freezing onset by one-third compared to controls in low temperatures, with a detachment time also reduced by one-third, indicating excellent corrosion and ice resistance. The methylphenyl silicone resin had good anti-corrosion and anti-ice properties, with a low corrosion current density (i_corr) of 0.8793 μA/cm² and a high charge transfer resistance (R_ct) of 24,930 Ω·cm² in saline. Full article

In this study, the fatigue strength of polished drill pipe specimens was investigated and compared with previous test results of corroded and not-corroded pipes. The resonant fatigue test rig, which was designed and implemented by the University of Pisa, is initially presented by providing a detailed description of the set-up of the machine, the calibration of the strain gauges, the control system, and the correct identification of the vibrational node locations. A polishing rig was also designed and put into operation to remove the corrosion pits from the outer surface of almost the entire length of the drill pipe specimens. After the fatigue tests with the resonant rig, and the observation of the fatigue fracture of the specimens, a few samples were extracted from different zones (corroded and not corroded) of the failed drill pipe specimens. This allowed for investigations to be carried out using a scanning electronic microscope. The obtained results were analyzed using the Murakami model, and a discussion is presented about the effect of the corrosion pits on the fatigue strength. Full article

Fractures are the main reservoir space in basement weathering crusts and control the development of dissolution/alteration pores. A clear understanding of the main factors controlling fracture formation is needed to accurately predict reservoir characteristics. In this study, the reservoir characteristics along with the vertical zonation and thermal history of basement weathering crust were studied through lithology, mineral identification, porosity and permeability tests, nuclear magnetic resonance (T₂), whole-rock analysis, and fission-track dating based on core samples, cuttings, and imaging logging data. Under the constraints of the Anderson model, the formation stages and timing of fractures were analyzed according to the regional stress field, fracture strike, fracture filling characteristics, and rock mechanical properties. The results revealed tensile structural fractures, shear structural fractures, weathering micro-fractures, alteration fractures, and intracrystalline alteration pores in the weathering crust of the Pre-Cenozoic basement in Lishui Sag. The reservoirs were characterized by low porosity, low permeability, and small pore diameter. The reservoir quality of granite was better than that of gneiss. The weathering crust could be divided into four zones: the soil layer, weathering dissolution zone, weathering fracture zone, and bedrock zone. The thickness of the soil layer and weathering dissolution zone were small. Four stages of fractures were identified: Yandang movement shear fractures, Paleocene tension structural fractures, Huagang movement shear fractures, and Longjing movement shear fractures. The main stage of basement fracture formation differed between the Lingfeng buried hill zone and Xianqiao structural zone. Considering the influence of the temperature and pressure environment on the rock’s mechanical properties, the differential fracture formation is related to the lithology, the coupling between the uplifted and exposed basement histories, and the tectonic stress field. Combined with the thermal histories of the Lingfeng buried hill zone and Xianqiao structural zone, the results suggest that the Lingfeng buried hill granite is favorable for basement fractures in Lishui Sag. Overall, this paper provides a novel method for analyzing the stages of fracture formation. Full article

The generation of hydro-mechanical resonance is related to the transition of the boundary layer and the development of vortex shedding. The application effect of suction control in hydrodynamics is equally deserving of consideration as an active control technique in aerodynamics. This study examines how suction control affects the flow field of the NACA0009 blunt trailing edge hydrofoil using the γ transition model. Firstly, the accuracy of the numerical method is checked by performing a three-dimensional hydrofoil numerical simulation. Based on this, three-dimensional hydrofoil suction control research is conducted. According to the results, the suction control increases the velocity gradient in the boundary layer and delays the position of transition. The frequency of vortex shedding in the wake region lowers, and the peak value of velocity fluctuation declines. The hydrofoil hydrodynamic performance may be successfully improved with a proper selection of the suction coefficient via research of the suction coefficient and suction position on the flow field around the hydrofoil. The lift/drag ratio goes up as the suction coefficient goes up. The boundary layer displacement thickness and momentum thickness are at their lowest points, and the velocity fluctuation amplitude in the wake region is at its lowest point as the suction coefficient C_μ = 0.003. When the suction slots are at the leading edge, the momentum loss in the boundary layer is minimal and the velocity fluctuation in the wake zone is negligible. Full article

Back pain (BP) due to degenerative disc disease (DDD) is a severe, often disabling condition. The aim of this study was to determine the association between the expression level of proinflammatory cytokines (IL-1β, IL-6, and IL-17), angiogenesis markers (VEGF-A and CD31) in intervertebral disc (IVD) tissue and IVD degeneration in young people with discogenic BP. In patients who underwent discectomy for a disc herniation, a clinical examination, magnetic resonance imaging of the lumbar spine, histological and immunohistochemical analyses of these factors in IVD were performed in comparison with the parameters of healthy group samples (controls). Histology image analysis of IVD fragments of the DDD group detected zones of inflammatory infiltration, combined with vascularization, the presence of granulation tissue and clusters of chondrocytes in the tissue of nucleus pulposus (NP). Statistically significant increased expression of IL-1β, IL-6, IL-17, VEGF-A and CD31 was evident in the samples of the DDD group compared with the controls, that showed a strong correlation with the histological disc degeneration stage. Our results denote an immunoinflammatory potential of chondrocytes and demonstrates their altered morphogenetic properties, also NP cells may trigger the angiogenesis. Full article

In this study, a resonant bending fatigue test rig, designed and implemented by the University of Pisa, is presented, providing a detailed description of the set-up of the machine, the strain gauges calibrations, and the control system used with the main electronic devices. Several geometries of drill pipe connections and pipe samples made of different materials were tested, and all the obtained experimental fatigue results are presented in the paper and compared to previous experimental data. Fractographic images are provided to clearly show that, in two kinds of drill pipe connections, the crack initiation was found at the connection zone, whereas for another connection geometry, it was found at the pipe body. In order to interpret these latter results, a discussion about the section modulus of bending of the various sections of the drill pipes was provided, along with an FE model of a specific zone of one of these connections. Full article

To study the aerodynamic characteristics of the convex structure of a surface-monitoring device on a high-speed train and to evaluate its impact on the aerodynamic performance of the high-speed train, numerical simulation research was conducted on three different layouts of the monitoring device. The computational fluid dynamics (CFD) method was used for the simulation study, and the unsteady compressible NS equation was used as the control equation. Hexagonal grid technology was used to reduce the demand for the grid quantity. The rationality of the grid size and layout was verified through grid independence research. To increase the accuracy of the numerical simulation, the γ-Re_θ transition model and improved delayed detached eddy simulation (IDDES) method were coupled for the simulation research. The aerodynamic characteristics of the different operation directions and configurations were compared and analyzed. The research results showed that the windward side of the single pantograph detection device experienced positive pressure, and the sideline and leeward sides experienced negative pressure. Increasing the fillet radius of the sideline could appropriately reduce the aerodynamic resistance. When the speed was about 110 m/s, the drag force coefficient of the detection device was 210~410 N, and the lateral force was small, which means that it had little impact on the overall aerodynamic force of the train. According to the results of the unsteady analysis of the layout with a large space, the resistance during forward travel was greater than that during negative travel. The streamlined upwind surface was conducive to reducing the scope of the leeward separation zone and the amplitude of the pressure fluctuation in the leeward zone, and it thus reduced the resistance. For the running trains, a vortex was formed on their leeward surface. The pressure monitoring results showed that the separated airflow had no dominant frequency or energy peak. The possibility of the following train top and other components experiencing resonance damage is low. Full article

The vibro-acoustic performance of a fluid-loaded periodic locally resonant (LR) plate was examined in this research, with a specific focus on the effect of water fluid on the vibration and sound radiation of the LR structure. The analytical models of the fluid-loaded LR plate’s band gap, vibration, and acoustic radiation were theoretically derived with closed-form solutions, which can be used to predict the general vibro-acoustic rules of underwater LR structure. The results show that the LR band-gap width and Bragg frequency are significantly reduced when water fluid is considered. Besides, the frequency range that can be tuned to control the vibration and sound radiation for the LR plate with fluid is much narrower than that without fluid. The reason for inducing the above effects was also given in this research, which can be physically explained by the attached mass caused by the water fluid. In addition, the reason for the enhanced radiation efficiency close above the band gap was also discussed, which is caused by the change of radiation mode from corner or edge radiation to monopole radiation. Furthermore, adding small damping into the resonator could reduce the vibration and sound radiation in the frequency range above or close below the band gap, inducing the attenuation zone to be significantly broadened. Thus, designing the periodic resonators with proper damping could be an efficient method to make the LR plate more beneficial for vibration and noise reduction in water-surrounding applications. Full article

The power oscillation induced by pressure fluctuation in the draft tube of the hydraulic turbine is one of the limiting factors preventing the Francis turbine from operating in the vibration zone. At the present power grid with a high proportion of renewable energy resources, we try to improve the load regulation ability of the hydropower units by extending the stable operation zone to the vibration zone. By the mathematical modelling of pressure fluctuation, this paper gives an analytical expression of the power oscillation. We derive the extended Hamiltonian model of the hydropower unit where power oscillation is external excitation. Secondly, the damping injection method introduces some desired interconnection and damping matrices as the Hamiltonian damping factor into the additional damping control. Finally, through theoretical analysis and experimental simulation, this research discusses the resonance characteristics of pressure fluctuation and power oscillation, the equivalent analysis between the damping factor and equivalent damping coefficient, and the control design of vibration zone crossing during the start-up. Simulation results show that when r₂₅ = 1.3, the minimum power oscillation amplitude is 0.5466, which is equivalent to an increase in D by 20. The maximum oscillation amplitude decreases by 4.6%, and the operation limited zone is reduced by 10.1%. The proposed additional damping control can effectively suppress the power oscillation and expand the regulation range. Full article