Search Results (128)

This paper proposes wideband circularly polarized (CP) 1-D connected array antennas with slant slot feeders and gradient artificial dielectric layers (ADLs). The slant slot feeder introduces an identical electric field (E-field) along the x- and y-directions. Three slabs consisting of multiple ADLs are stacked above the slot feeder. Due to the different boundary conditions of a 1-D connected array in the $zx$- and $zy$-planes, the guided wave in the slabs exhibits different multipath lengths along the x- and y-directions, leading to a 90° phase difference between the $E_x$ and $E_y$ components. Moreover, the cascaded slabs are designed with gradient effective permittivities for a gradual impedance transition from the guided mode to the radiating mode, allowing for wideband matching and CP performance. To validate the proposed design approach, an 8 × 1 array was fabricated and measured. The antenna shows a 1.96:1 (10.1–20 GHz) impedance bandwidth (VSWR < 2) and a 1.46:1 (12–17.5 GHz) 3 dB axial ratio bandwidth in measurement. The array exhibits an average right-hand CP boresight gain of 12.39 dBic. Moreover, we produced a frequency-invariant beam pattern with an average half-power beamwidth (HPBW) of 24.77° and a standard deviation below 3.63° over 12–18 GHz for the target pattern, with a HPBW of 26°, demonstrating wideband electronic warfare performance using the proposed array. Full article

This article presents a numerical study of the influence of applied nonlinearities on the response of a flat slab–column structure under progressive collapse conditions. A key aspect of the work is the extension of nonlinear static analysis by considering cases of material nonlinearity combined with both linear and nonlinear geometry, using a corotational formulation and a damage-based elasto-plastic concrete model. A multi-layer shell element implemented in the OpenSees platform is used to distinguish between the strength characteristics of the concrete and reinforcement, with particular attention given to the modeling of the slab–column connection in nonlinear analyzes involving both shell and beam elements. The applied vertical pushover analysis enabled the derivation of load–displacement curves and the identification of the sequence in which plastic hinges can be formed. The development of membrane action resistance, expressed through the formation of compressive and tensile rings, is observed numerically when both material and geometric nonlinearities are simultaneously considered. Moreover, the transition from compressive membrane action to tensile membrane action occurs once the deflections reach the value equal to the effective depth of the slab. This insight may serve as an important guideline for the development of future revisions to design standards related to progressive collapse. Full article

This study investigates the mechanical performance of concrete paving stones manufactured with recycled aggregates derived from TransMilenio slab demolition waste (CDW-A-TS) as a sustainable alternative to conventional natural coarse aggregates (river gravel) and fine aggregates (river sand). Construction and demolition waste from Bogotá’s mass transit system slabs was processed to produce recycled aggregates, which were replaced at substitution levels of 0%, 30%, 50%, and 100% by volume of natural aggregates. The mechanical properties evaluated included compressive strength, flexural strength, abrasion resistance, and water absorption, following Colombian Technical Standards (NTC) and international protocols. Results demonstrate that all CDW-A-TS mixtures exhibit enhanced compressive strength, with improvements ranging from 14.71% to 32.82% compared to the control mix. Flexural strength also increased by 1.34% to 6.13%. However, water absorption increased proportionally with CDW-A-TS content (10.66% to 25.24%). The optimal substitution level was identified at 30% CDW-A-TS based on a composite evaluation of mechanical performance (compressive and flexural strength), durability indicators (water absorption and abrasion resistance), This research demonstrates the technical viability of incorporating TransMilenio demolition waste in paving stone production, contributing to circular economy principles and sustainable urban infrastructure development. This finding aligns with prior research affirming the viability of incorporating recycled coarse aggregates in concrete prefabricates, such as paving stones, for various construction applications. Full article

The Central Asian Orogenic Belt (CAOB) represents a crucial area for understanding the tectonic evolution of the Paleo-Asian Ocean and surrounding orogenic systems. This study investigates the petrology, geochronology, and geochemistry of volcanic and clastic rocks from Well HFD3 in the northern Songliao Basin, which provides key insights into the tectonic development of this region. Zircon U–Pb dating of tuff samples from the Linxi Formation provides an accurate age of 251.1 ± 1.1 Ma, corresponding to the late Permian. Geochemical analyses show that the clastic rocks are rich in SiO₂ (63.5%) and Al₂O₃ (13.7%), with lower K₂O/Na₂O ratios (0.01–1.55), suggesting low compositional maturity. Additionally, the trace element data reveal enrichment in light rare earth elements (LREEs) and depletion in Nb, Sr, and Ta, with a negative Eu anomaly, which indicates a felsic volcanic arc origin. The Chemical Index of Alteration (CIA) values (53.2–65.8) reflect weak chemical weathering, consistent with cold and dry paleo-climatic conditions. These findings suggest that the Linxi Formation clastic rocks are derived from felsic volcanic arcs in an active continental margin environment, linked to the subduction of the Paleo-Asian Ocean slab. The sedimentary conditions reflect a gradual transition from brackish to freshwater environments, corresponding with the final stages of subduction or the onset of orogeny. Full article

Flat slab structures are extensively utilized in modern construction owing to their efficient load transfer mechanisms and optimized space utilization. Nevertheless, the persistent issue of brittle punching shear failure at connection zones continues to pose significant engineering challenges. This study proposes an innovative cross-shaped steel-reinforced concrete (SRC) column–slab connection. Through combining test and numerical analyses, the failure mechanisms and performance control principles are systematically analyzed. A refined finite element model incorporating material nonlinearity, geometric characteristics, and interface effects is developed, demonstrating less than 3% error upon test validation. Using the validated model, the influence of key parameters—including concrete strength (C30–C60), reinforcement ratio (ρ = 0.65–1.77%), shear span–depth ratio (λ = 3–6), and limb height-to-thickness ratio (c₁/c₂ = 2–4)—on the punching shear behavior is thoroughly investigated. The results demonstrate that increasing concrete strength synergistically improves both punching shear capacity (by up to 49%) and ductility (by 33%). A critical reinforcement ratio threshold (0.8–1.2%) is identified. When exceeding this range, the punching shear capacity increases by 12%, but reduces ductility by 34%. Additionally, adjusting the shear span–depth ratio enables controlled failure mode transitions and a 24% reduction in punching shear capacity, as well as a 133% increase in displacement capacity. These results offer theoretical support for the design and promotion of this novel structural system. Full article

The El Bola mafic–ultramafic intrusion (EBMU) in Egypt’s Northern Eastern Desert represents an example of Neoproterozoic post-collisional layered mafic–ultramafic magmatism in the Arabian–Nubian Shield (ANS). The intrusion is composed of pyroxenite, olivine gabbro, pyroxene gabbro, pyroxene–hornblende gabbro, and hornblende-gabbro, exhibiting adcumulate to heter-adcumulate textures. Mineralogical and geochemical analyses reveal a coherent trend of fractional crystallization. Compositions of whole rock and minerals indicate a parental magma of ferropicritic affinity, derived from partial melting of a hydrous, metasomatized spinel-bearing mantle source, likely modified by subduction-related fluids. Geothermobarometric calculations yield crystallization temperatures from ~1120 °C to ~800 °C and pressures from ~5.2 to ~3.1 kbar, while oxygen fugacity estimates suggest progressive oxidation (log fO₂ from −17.3 to −15.7) during differentiation. The EBMU displays Light Rare Earth element (LREE) enrichment, trace element patterns marked by Large Ion Lithophile Element (LILE) enrichment, Nb-Ta depletion and high LILE/HFSE (High Field Strength Elements) ratios, suggesting a mantle-derived source that remained largely unaffected by crustal contribution and was metasomatized by slab-derived fluids. Tectonic discrimination modeling suggests that EBMU magmatism was triggered by asthenospheric upwelling and slab break-off. Considering these findings alongside regional geologic features, we propose that the mafic–ultramafic intrusion from the ANS originated in a tectonic transition between subduction and collision (slab break-off) following the assembly of Gondwana. Full article

Under the impetus of achieving global sustainable development goals, the civil construction industry is accelerating its transition towards high-quality, green, and low-carbon practices. Prefabricated, modular building technology has become a key tool due to its advantages in energy conservation, emission reduction, and shortened construction periods. However, existing research on the seismic performance of prefabricated, modular, reinforced concrete column–beam (RCS) composite structures often focuses on the construction form of beam–column joints, paying less attention to the impact of floor slabs on the seismic performance of joints during earthquakes. This may make joints a weak link in structural systems’ seismic performance. To address this issue, this paper designs a prefabricated, modular RCS composite joint considering the effect of floor slabs and uses the finite element software ABAQUS 2023 to perform a quasi-static analysis of the joint. The reliability of the method is verified through comparisons with the experimental data. This study examines various aspects, including the joint design and the material’s constitutive relationship settings, focusing on the influence of parameters, such as the axial compression ratio and floor slab concrete strength, on the joint seismic performance. It concludes that the seismic performance of the prefabricated, modular RCS composite joints considering the effect of floor slabs is significantly improved. Considering the composite effect of the slabs, the yield loads in the positive and negative directions for node FJD-0 increased by 78.9% and 70.0%, respectively, compared to that of the slab-free node RCSJ3. The ultimate bearing capacities improved by 13.2% and 9.98%, respectively, and the energy dissipation capacity increased by 23%. Additionally, the variation in the axial load ratio has multiple effects on the seismic performance of the joints. Increasing the slab thickness significantly enhances the seismic performance of the joints under positive loading. The bolt pre-tensioning force has a crucial impact on improving the bearing capacity and overall stiffness of the joints. The reinforcement ratio of the slabs has a notable effect on the seismic performance of the joints under negative loading, while the concrete strength of the slabs has a relatively minor impact on the seismic performance of the joints. Therefore, the reasonable design of these parameters can optimize the seismic performance of joints, providing a theoretical basis and recommendations for engineering application and optimization. Full article

As a by-product of phosphate fertilizer production, phosphogypsum (PG) poses pressing environmental challenges that demand urgent resolution. To address the research gap in dynamic impact behavior of PG-modified concrete (PGC), this study developed truss-reinforced PGC slabs (PG volumetric fractions: 0% and 2%) and evaluated their impact resistance through drop-weight tests from a 3.75 m height. A systematic parametric investigation was conducted to quantify the effects of slab thickness (100–120 mm), steel plate reinforcement at the tension zone, PG content, and impact cycles. Experimental results revealed that increasing slab thickness to 120 mm reduced mid-span displacement by 13%, while incorporating steel plate reinforcement provided an additional 5.3% reduction. Notably, PG addition effectively suppressed crack propagation, transitioning failure modes from radial fracture patterns to localized mid-span damage. Finite element modeling ABAQUS (2022) validated experimental observations, demonstrating strong agreement. While optimized PG dosage (2%) exhibited limited influence on impact resistance, it enhanced PG utilization efficiency by 18%. Combined with increased slab thickness (displacement reduction: 13%), this study establishes a design framework balancing environmental sustainability and structural reliability for impact-resistant PGC applications. Within the framework of truss-reinforced concrete slabs with constant PG dosage, this study established a numerical model for geometric parameter modulation of impactors. Through systematic adjustment of the drop hammer’s contact width (a) and vertical geometric height (h), a dimensionless control parameter—aspect ratio c = h/a (0.2 ≤ c ≤ 1.8)—was proposed. Nonlinear dynamic analysis revealed that the peak impact load demonstrates an inverse proportional functional decay relationship with increasing c, yielding an empirical predictive model. These parametrized regularities provide theoretical foundations for contact interface optimization in impact-resistant structural design. Full article

Snow avalanches occur in snow-covered highland mountains and represent one of the most significant natural hazards pertaining to the field of geoscience. Although some insight into the formation of avalanches has been provided, a comprehensive overview or critical review of the latest research is currently lacking. This paper reviews recent advances on the formation process of dry slab avalanches and provides a guiding framework for further research. The formation of avalanches is the consequence of a series of fracture processes in the snowpack, which is usually induced by the failure of a weak layer underlying a snow slab layer. The parameters at each stage of avalanches’ formation are reviewed from theoretical, experimental and simulation perspectives. In terms of the onset of crack propagation, the understanding of the mechanical process has gone through a transition from shear theory, to the anticrack model and supershear. The critical length shows divergent trends with snowpack parameters and slope angles, and there is a lack of consensus in different models. The specific fracture energy is also an essential component in determining fracture propagation. Within cracks’ dynamic propagation, the crack propagation speed includes both the sub-Rayleigh regime and supershear. The crack speed exceeds the shear wave speed in the supershear mode. When the crack propagation reaches a specific distance, the slab undergoes a tensile fracture and the cracking’s arrest. The numerical simulation allows a complete reproduction of the initial failure, the crack’s dynamic propagation and slab fracture. In the future, a unified model is necessary through refining the formative mechanism and integrating it with the avalanche flow. This work offers a comprehensive understanding of the mechanics of the formation and release of avalanches, useful for both modelers and experimentalists. Full article

La-doped Li_1.2Ni_0.13Mn_0.54Co_0.13O₂ cathode materials were successfully synthesized by the sol-gel method. The structure, morphology, element valence states, cyclic voltammetry, and cyclic properties were characterized to investigate the properties of the synthesized materials. The as-prepared La-doped Li_1.2Ni_0.13Mn_0.54Co_0.13O₂ materials exhibit well the crystalline hexagonal layered structures with lamellar-like particles featuring a rough surface. The optimal sample, designated as LLRMO-2 with 1/100 La³⁺ doping, delivers an impressive discharge capacity of 271.2 mAh g⁻¹ with a capacity retention of 87.8% after 100 cycles at the current density of 100 mA g⁻¹ compared with that of 203.5 mAh g⁻¹ with only 110.6 mAh g⁻¹ after 100 cycles for the pristine sample. Furthermore, the LLRMO-2 cathode exhibits a superior rate capability compared to the pristine sample and shows excellent cyclic performances with the capacity retention of 48.1% after 400 cycles. The voltage decay per cycle is only 1.60 mV, which is less than 3.70 mV of the pristine one. The enhanced capacity, rate capability, and cyclic performance observed in the La-doped Li-rich layered cathode can be attributed to the improved structural stability as well as the higher diffusion coefficient of lithium ions. These results suggest that the strategy of introducing La³⁺ into the transition metal slabs is an efficient approach for boosting electrochemical performances of Li-rich Mn-based cathode materials via enhancing structural stability. Full article

The spatial distribution of equiaxed crystal zones during extra-thick slab solidification exerts a critical influence on the mechanical performance of the final product. This investigation establishes a dual-pathway control framework for solidification structure modulation, differentiating between intrinsic regulation through columnar-to-equiaxed transition (CET) positioning and extrinsic intervention via strand electromagnetic stirring (S-EMS) parameter adjustment. The aim is to improve the internal quality of extra-thick slabs, enabling further investigations into the material properties. To achieve this, a solidification heat transfer model along with a cellular automata–finite element model were developed to characterize the thermal conditions at CET initiation, with experimental validation conducted on a 475 mm extra-thick slab. The systematic analysis identified a significant correlation between continuous casting parameters, alloy concentrations, and CET positioning, while S-EMS experiments further elucidated the distribution patterns of the solidification structure and the formation mechanism of the white band in the mushy zone. This methodology bridges computational metallurgy with process engineering, offering systematic guidance for solidification structure control in extra-thick slabs. Full article

The Yana–Kolyma collision orogen, Eastern Siberia, is one of world-class gold economic belts, where large gold deposits are localized, mainly in the Upper Paleozoic and Lower Mesozoic clastic rocks. Dike-hosted orogenic gold deposits are found and to a lesser extent studied, but they are important for understanding the structural control of mineralization within the framework of the orogen. Orogenic gold deposits of the Vyun ore field are hosted in Kimmeridgian–Titonian mafic, intermediate and felsic dikes, but they have no genetic connection with dikes. The late formation of deposits led to the fact that previously reactivated polydeformed structures were subsequently mineralized. The study of the structural control of mineralization is also complicated by superimposed late tectonic events. Based on the analysis of collected field materials, this paper presents the results of the study of deformation structures of the Vyun ore field within the framework of the Mesozoic evolution history throughout the geological time of the eastern convergent margin of the Siberian Craton. Four stages of deformations are identified. The pre-mineralization deformations and metamorphic and magmatic events share a common NE-SW shortening (D1 phase), which is related to the subduction of the Oymyakon oceanic slab and collision of the Kolyma–Omolon superterrane from the eastern margin of the Siberian Craton. This first stage is characterized by the superposition of several tectonic events under conditions of compression and progressive deformations (D1/1 and D1/2). Ore mineralization was formed at the end of compression in the same stress field (D1/2). Its structural control is determined by reactivation of older dikes and faults. Dikes are areas of heterogeneous stress and heterogeneous strain, being favorable for the concentration of ore fluids. The metallogenic time of formation of the gold mineralization is synchronous with the tectonic event, which likely reflects the final stages of the Kolyma–Omolon microcontinent–Siberian Craton collision of the Valanginian during crustal thickening. The main impulse of the Au mineralization D1/2 phase coincided with a slowdown in convergence. The post-mineralization tectonic regime was related to the Aptian–Late Cretaceous tectonic transition from compression to transpression. Transpressional tectonics were determined accordingly by W-E (D2 phase) and N-S (D3 phase) stress fields caused by several accretion events in the Cretaceous on the northern and eastern margins of Siberia. D4 phase extensional structures were caused by the opening of the Eurasian Oceanic basin in the Arctic in the Paleocene. The obtained results have a first-order impact on the understanding of the structural control of orogenic gold deposits and their relationship to the evolution of the host orogen. The new findings improve the tectonic knowledge of an area of interest for ore deposit exploration targeting orogenic gold deposits in Phanerozoic terranes of craton margins. Full article

Superdeep diamonds and their syngenetic inclusions are crucial for understanding Earth’s deep carbon cycle and slab–mantle redox dynamics. The origins of these diamonds, especially their links to iron (Fe) carbides and ferropericlase with varying Mg# [=Mg/(Mg+Fe)_at], however, remain elusive. In this study, we performed high pressure–temperature (P-T) experiments (10–16 GPa and 1200–1700 K) across cold-to-warm subduction zones using a multi-anvil press. The results reveal a stepwise Fe-mediated carbonate reduction process for the formation of superdeep diamonds: MgCO₃ → Fe-carbides (Fe₃C/Fe₇C₃) → graphite/diamond. This mechanism explains two phenomena regarding superdeep diamonds: (1) anomalous ¹³C depletion results from kinetic isotope fractionation during ¹²C enrichment into the intermediate Fe-carbides; (2) nitrogen scarcity is due to Fe-carbides acting as nitrogen sinks. Ferropericlase [(Mg,Fe)O] formed during the reactions in our experiments shows Mg# variations (0.2–0.9), similar to those found in natural samples. High Mg# (>0.7) variants from lower temperature experiments indicate diamond crystallization from carbonatitic melts in the shallow lower mantle, while the broad Mg# range (0.2–0.9) from experiments at higher temperatures suggests multi-depth formation processes as found in Brazilian diamonds. These findings suggest that slab–mantle interactions produce superdeep diamonds with distinctive Fe-carbides and ferropericlase assemblages as inclusions, coupled with their ¹³C- and nitrogen-depleted signatures, which underscore thermochemical carbon cycling as a key factor in deep carbon storage and mantle mineralogy. Full article

This work introduces a 0.6-scale water model of the continuous slab-casting process and a MATLAB-based model to study the effects of non-primed and multiphase flow on pressure and flow rate. The water model uses stopper-rod flow control and features pressure and velocity measurements at multiple locations. The new computational model, PFSR V4 (Pressure-drop Flow-rate model of Stopper Rod metal delivery systems, Version 4), improves upon a prior one-dimensional Bernoulli-based framework by incorporating a bubble accumulation zone. This zone represents a region of bubbly flow with an intermediate gas fraction between constant-pressure gas pockets below the stopper tip and the downstream bubbly flow regime. Parametric studies with the water model show that flow remains fully primed at low gas flow rates but transitions to non-primed flow as the gas flow rate exceeds 10–16 SLPM. Three different flow regions are observed inside the water model nozzle: air pocket, bubble accumulation, and bubbly flow, which are also captured by the new computational model. Above a critical gas flow rate, the flow becomes unstable and difficult to control, though higher hot gas flow rates are expected for similar transitions in a real steel caster due to gas expansion at high temperatures. Pressure changes are minimal in the air pocket region and increase significantly in the upper bubble accumulation zone, where liquid velocity is much higher than in the classic bubbly-flow region, found lower in the nozzle. The new model was successfully calibrated to match the observed flow regimes and shows good agreement with the water-model measurements. Full article

Optical absorption spectra of 9 MeV electron-irradiated GaSe crystals measured at temperatures in the range from 9.5 to 300 K were analyzed. The absorption spectra with features caused by Ga vacancies in two charge states and direct interband transitions were fitted by a model equation. Temperature dependencies of the defect concentrations and optical transition energies, as well as of the GaSe band gap, were determined. Current- and capacitance-voltage characteristics and DLTS spectra were measured for as-grown and electron-irradiated GaSe slabs with Sc (barrier) and Pt (ohmic) contacts. An experimental Sc/GaSe Schottky barrier height of 1.12 eV was determined in close agreement with a theoretical estimate. The activation energy and the hole capture cross-section deduced from the DLTS data are 0.23 (0.66) eV and 1.5 × 10⁻¹⁹ (2.3 × 10⁻¹⁵) cm⁻² for the supposed $V_{\mathrm{Ga}}^{-1}$ ($V_{\mathrm{Ga}}^{-2}$) defect. For the electron-irradiated GaSe crystals, the found activation energies are close to the values inferred from the optical measurements. Full article