Search Results (1,112)

In this study, density functional theory (DFT) within the generalized gradient approximation (GGA) is employed to investigate the structural, electronic, mechanical, and thermoelectric properties of perovskite hydrides XZrH₃ (X = Mg, Ca, Sr, Ba). Mechanical stability and ductility are evaluated through the Cauchy pressure, Pugh’s ratio, and Poisson’s ratio, all of which point to ductile behavior with a dominant ionic-bonding character. Electronic structure calculations reveal metallic behavior arising from band overlap at the Fermi level. Equilibrium energy–volume data are fitted with the Murnaghan equation of state, and transport coefficients are extracted using the BoltzTraP package as implemented in WIEN2k. The absence of a band gap and the overlap between valence and conduction bands confirm conductor-like behavior. Lattice thermal conductivity for MgZrH₃, CaZrH₃, SrZrH₃, and BaZrH₃ increases monotonically with temperature. Overall, the results identify MgZrH₃ in particular as a promising candidate for thermoelectric devices and solid-state hydrogen storage, thereby supporting progress toward a sustainable hydrogen economy. Full article

In this paper I study a two-dimensional discrete-time evolutionary logistic-type model describing the coupled dynamics of population density and a continuously evolving trait. I provide a local bifurcation analysis of the equilibria, deriving explicit conditions for their existence and local stability. In particular, I show that the boundary and interior equilibria exchange stability through a transcritical bifurcation, and I characterize analytically the subsequent loss of stability of the interior equilibrium via period-doubling and Neimark–Sacker bifurcations. Transversality is established in all cases, and the criticality of the bifurcations is determined through normal form and Lyapunov coefficient computations. I show that the period-doubling bifurcation can be supercritical or subcritical, while the Neimark–Sacker bifurcation is generically nondegenerate and may be either supercritical or subcritical, depending on parameter values. Full article

Many complex systems, particularly glasses and disordered materials, exhibit energy landscapes with exponentially many metastable states. Such landscape structure strongly influences equilibrium behavior but is not explicitly represented in standard thermodynamic state spaces. We develop a constrained equilibrium framework in which configurational complexity, defined as the logarithmic density of metastable basins, is treated as an additional macroscopic coordinate. Starting from maximum entropy with simultaneous constraints on energy and complexity, we obtain a generalized Gibbs ensemble characterized by a conjugate bias parameter. Standard thermodynamic structure remains intact, with extended relations arising as constrained equilibrium identities. A mean-field glassy example with explicit complexity function demonstrates how complexity bias shifts the saddle-point structure of the partition function and modifies equilibrium response functions. The geometric formulation further provides a diagnostic of landscape reorganization within an enlarged state space. This framework offers a systematic equilibrium description of how energy-landscape structure influences thermodynamic behavior in systems with rugged configuration spaces. Full article

Multi-material structures based on titanium alloys represent a promising approach for the fabrication of functionally graded orthopedic implants capable of combining high mechanical strength with reduced stiffness to minimize the stress-shielding effect. In the present work, multi-material Ti15Ta/Ti6Al4V specimens were fabricated by laser powder bed fusion (L-PBF) for the first time, and the processing parameters of the transition zone were systematically optimized. Three regimes were investigated: baseline (93 J/mm³), double scanning (186 J/mm³), and reduced speed (116 J/mm³). The microstructure and elemental distribution were examined by SEM and EDS; mechanical properties were evaluated through tensile testing and microhardness measurements; biocompatibility was assessed using osteoblasts and gingival fibroblasts. The double scanning regime provided the highest density of the transition zone (99.49%). Tensile failure of the specimens occurred in the Ti15Ta region, confirming the quality of the metallurgical bond. The ultimate tensile strength ranged from 534 to 543 MPa with an elongation at break of 15.7–16.4%. Heat treatment at 875 °C led to the formation of an equilibrium lamellar microstructure and smoothing of the interface. Cell viability on both alloys exceeded 88% as confirmed by flow cytometry and remained above the 70% non-cytotoxicity threshold defined by ISO 10993-5. The obtained results demonstrate the technological feasibility of fabricating multi-material Ti15Ta/Ti6Al4V structures and achieving high-quality metallurgical bonding, which constitutes a necessary first step toward the development of functionally graded orthopedic implants. Full article

Carbonate reservoirs, characterized by extensive fractures and cavities, are prone to gravity displacement during drilling when the bottom-hole pressure approaches equilibrium. This phenomenon, driven by density differences between drilling and formation fluids, can result in simultaneous overflow and leakage, posing significant well control risks such as kicks or blowouts. The occurrence of gravity displacement downhole makes its timely detection through conventional annular flow monitoring techniques challenging. This study investigates the triggering conditions and safe density window for gravity displacement in fractured and cavernous formations. Through theoretical analysis and experimental simulation, we examined the displacement mechanisms in both fractured and cavernous conditions. Computational fluid dynamics (CFDs) simulations were used to validate critical fluid column heights for fractured formations and the proposed safe density window. Based on these findings, practical methods to mitigate the hazards associated with gravity displacement overflow are proposed. The results offer valuable guidance for the field identification and mitigation of such incidents, contributing to managed pressure drilling and enhancing drilling safety in complex carbonate reservoirs. Full article

In geotechnical engineering, operations such as foundation pit excavation, slope cutting, and tunnel boring often involve lateral unloading under plane strain conditions. This unloading pattern exhibits significant differences from the traditional axisymmetric triaxial loading path. To investigate the mechanical behavior of silt under such conditions, a series of plane strain tests were conducted using a self-designed plane strain apparatus, focusing on both vertical loading (constant lateral stress) and lateral unloading (constant vertical stress) paths. The results indicate that the failure of soil during unloading can be identified as the stage where the vertical deformation rate first increases and then decreases, corresponding to a distinct inflection in the stress–strain curve. The internal friction angle remained essentially constant regardless of the stress path, dry density, or consolidation stress ratio, while cohesion was higher under loading than under unloading. Failure deviatoric stress increased linearly with vertical consolidation stress and was unaffected by the consolidation stress ratio. The classical limit equilibrium condition remains valid for unloading under both isotropic and anisotropic consolidation. These findings provide a practical criterion for failure detection and highlight the necessity of adopting plane strain parameters in the design of lateral unloading engineering works. Full article

Octa(3,3,3-trifluoropropyl) polyhedral oligomeric silsesquioxane (8F-POSS) was synthesized via a vertex-capping method and incorporated into natural rubber (NR) and deproteinized natural rubber (DPNR) to fabricate inorganic–organic vulcanizates. Curing characteristics, crosslink density, and the filler–rubber interaction parameter (α) were evaluated. We found that 8F-POSS retarded vulcanization kinetics but eventually enhanced network integrity. Two-dimensional infrared (2D-IR) spectroscopy indicated a hydrogen-bond shielding effect between siloxane cages and protein hydroxyl groups in NR. This interaction governed morphology development: proteins in NR acted as compatibilizers to improve initial POSS dispersion, though at high loadings they compromised reinforcement efficiency (α fell from 18.12 to 9.04). In contrast, DPNR vulcanizates showed stronger direct filler–rubber interactions, with higher α values (25.66–35.58) and a more constrained physical network. Despite a denser physical network, the 8F-POSS cages increased fractional free volume and promoted interfacial frictional slippage, leading to a synergistic “reinforcement–dissipation” effect. As a consequence, 8F-POSS/DPNR vulcanizates exhibited an enhanced damping performance (e.g., a loss factor of 1.26) alongside a depressed Tg, reduced equilibrium swelling in oil from 324% to 147%, high hydrophobicity (water contact angle above 120°), and distinctive multi-stage thermal stability. These findings demonstrate a strategy to manipulate the protein network in NR using nanoscale hybrid fillers for the design of high-performance vulcanizates. Full article

Suppressing the polysulfide shuttle effect and accelerating the sulfur redox kinetics remain pivotal challenges for advancing the practical viability of lithium–sulfur batteries (LSBs). In this study, an iodine-doped carbon nitride (I-CN) material was synthesized via a one-step annealing strategy and employed as a metal-free sulfur cathode host. Compared to its pristine counterpart, I-CN exhibits a substantially increased specific surface area, which facilitates the homogeneous dispersion of sulfur species. More importantly, the incorporation of iodine atoms disrupts the equilibrium of the electron cloud distribution within the CN framework, leading to enhanced electron delocalization. This electronic modulation not only significantly improves the charge transport properties of carbon nitride but also strengthens the adsorption of lithium polysulfides (LiPS) and promotes Li₂S nucleation, thereby enabling fast and durable sulfur redox reactions. Benefiting from these synergistic effects, the S@I-CN electrode achieves high sulfur utilization, delivering an initial discharge capacity of 1341.9 mAh g⁻¹ at 0.1C. Even at a high current density of 5C, a remarkable reversible capacity of 472.7 mAh g⁻¹ is retained. Notably, the electrode retains 66.2% of its initial capacity after 800 cycles, demonstrating excellent long-term cycling stability. This halogen-based heteroatom doping strategy thus not only enhances the electrochemical performance of carbon nitride materials in LSBs through the rational manipulation of electron delocalization, but also offers a promising direction for the design of novel metal-free electrocatalysts in related energy conversion systems. Full article

Injection molding has been used for many years in the fabrication of thermoplastic parts with different complexities. With metal and ceramic injection molding, it is possible to realize at the end of the related process chain sintered metal and ceramic parts. Parts made from glass are rather seldom realized applying powder technology methods. This work describes the production of devices made from a commercial soda-lime glass applying the process chain of powder injection molding, covering the individual process steps like compounding, shaping, debinding, and sintering. In the first step, a binder consisting of polyethylene glycol (PEG) with different average molecular masses (4000, 8000, and 20,000 g/mol), polyvinyl butyral (PVB), and stearic acid (SA) were used for compounding new feedstocks with a solid load of 55 Vol% and 60 Vol%. As filler, a soda-lime glass with an average particle size of 6.1 µm, an almost symmetrical particle size distribution, a specific surface area of 0.78 m²/g, and a spherical morphology was applied. The measured equilibrium torque during compounding was low, with values between 2.5 and 5.5 Nm depending on the solid load and average molecular mass of the investigated PEG. All feedstock possessed a pseudoplastic flow behavior in the shear rate range between 10 and 3500 1/s. Small disk-shaped parts, as well as large cuboids and plates, were injection molded to a good quality. These green bodies were pre-debinded in water to remove the PEG, subsequently followed by thermal debinding to eliminate the remaining organic moieties. The concluding sintering in the temperature range between 660 and 680 °C delivered glass parts with huge density values close to 100% of the theoretical value, as measured by the Archimedes method. The principal feasibility of glass injection molding with a suitable feedstock system could be demonstrated successfully. Full article

The formation of recyclable polyethylene materials is significantly limited by traditional crosslinking methods, which involve solvent-heavy processes and permanent chemical bonds that cannot be undone. Herein, we report an environmentally friendly and scalable approach to construct a thermo-reversible polyethylene network (PE-g-DA) via solvent-free, one-step melt processing based on furan–maleimide Diels–Alder (D–A) dynamic covalent chemistry. Furan-functionalized polyethylene was dynamically crosslinked with bismaleimide during melt mixing, fully compatible with conventional polyolefin processing techniques. FTIR spectroscopy, temperature-dependent solubility, and differential scanning calorimetry collectively confirm the reversible formation and dissociation of D–A adducts, enabling thermal switching of the network structure. Equilibrium swelling experiments based on the Flory–Rehner model indicate that the crosslink density can be precisely controlled by varying the bismaleimide content. As a result, PE-g-DA exhibits significantly enhanced tensile strength while maintaining high ductility at moderate crosslink densities. Notably, the dynamic network allows efficient thermal reprocessing, with recycled samples retaining approximately 93% and 80% of their original tensile strength after the first and second reprocessing cycles, respectively. Moreover, intrinsic thermal self-healing behavior is directly visualized by scanning electron microscopy at 120 °C. This work demonstrates that combining dynamic Diels–Alder chemistry with solvent-free melt processing offers a practical and sustainable route to recyclable, reprocessable, and self-healable polyethylene materials with clear potential for large-scale industrial production. Full article

The momentum transport and scale-dependent motion characteristics within vegetation canopies play a crucial role in shaping near-surface turbulent structures and exchange processes, yet the interactions among different turbulent scales and their statistical representations remain insufficiently understood. Based on a series of controlled wind tunnel experiments, this study identifies coherent turbulent structures using a phase-space algorithm constructed from streamwise velocity fluctuation u′, acceleration a, and jerk j, and compares transport efficiency (exuberance η). This study uses scale-wise (cut-off frequency) momentum flux contribution analysis, natural visibility graph (NVG), and large–small-scale amplitude modulation to examine transport and multiscale behaviors across different canopy densities, array layouts, and inflow conditions. Results show that canopy density (different C_d drag coefficient) is a primary factor governing transport efficiency. Under low-wind staggered configurations, increasing canopy density strengthens the contribution of low-frequency large-scale motions to total momentum flux. In contrast, high-wind aligned configurations intensify canopy-top shear, enhancing small-scale motions and thereby reducing the relative contribution of large-scale motions. NVG analysis further reveals that in high-density canopies, large-scale acceleration and deceleration events tend toward equilibrium, whereas deceleration events dominate consistently in low- and medium-density cases. Amplitude modulation results indicate that high-density cases exhibit highly consistent modulation behavior, followed by low-density cases, while medium-density cases display a pronounced height-dependent variation, characterized by a distinct modulation critical point. This study proposes a unified analytical framework integrating coherent structure detection, graph-theoretic analysis, multiscale transport characterization, and large–small-scale modulation, providing a comprehensive description of momentum transport and scale motions within canopy flows, and it offers new insight into the mechanisms governing complex vegetation canopy turbulence. Full article

Water scarcity, rapid soil moisture loss, and high evaporative demand severely limit vegetable production in arid regions such as Qatar. Sustainable soil amendments that enhance water retention and stabilize plant water status are therefore critical for improving productivity. This study evaluated a biodegradable hydrogel synthesized from date-palm leaf cellulose using a sodium alginate crosslinking method and assessed its effects on soil hydro-physical properties and tomato (Solanum lycopersicum L.) performance under arid conditions. A pot experiment was conducted under semi-controlled conditions using a single-factor randomized complete design with three hydrogel rates (0, 1, and 2% w/w) and three replications, with one plant per pot. All treatments received the same seasonal irrigation depth, scheduled when soil moisture declined to approximately 60–65% of field capacity. The hydrogel exhibited rapid hydration behavior, reaching equilibrium within 30–60 min with a swelling ratio of 5.659 g g⁻¹, corresponding to a water uptake of 465.9%, and SEM analysis revealed a porous internal structure favorable for water retention. At 1 and 2% application rates, hydrogel significantly reduced bulk density, increased total porosity and field capacity, and maintained higher soil moisture across irrigation cycles. Tomato plants grown in hydrogel-amended pots showed substantial gains in fresh biomass and root length, together with higher chlorophyll content, leaf nitrogen concentration, and relative water content. Water use efficiency improved significantly at 1% hydrogel, whereas the 2% rate showed a positive but non-significant trend. Overall, the results demonstrate that hydrogels derived from date-palm waste can enhance soil water retention, plant physiological status, and tomato productivity, offering a locally relevant strategy to improve agricultural resilience in arid environments. Full article

Electrical Resistivity Tomography (ERT) has proven to be a highly sensitive geophysical method for characterizing the dynamics of seawater intrusion. This study uses tank experiments to simulate seawater intrusion, utilizing electrical resistivity tomography to monitor real-time changes in groundwater resistivity during the intrusion process. The objective is to quantitatively reveal the development and evolution mechanisms of seawater intrusion wedges in sandy aquifers, thereby establishing a real-time resistivity monitoring method for groundwater distribution and migration characteristics. This study improves resistivity imaging data processing methods, enhancing both efficiency and accuracy. The refined cross-hole ERT technique is applicable not only to meter-scale indoor experiments; its optimized forward and inverse algorithms can also be directly transferred to regional-scale field monitoring. Experimental results show that the average resistivity in the study area continuously decreases from 57 Ω·m in the initial freshwater state to 1.1 Ω·m at the intrusion stabilization point. Areas with resistivity values below 20 Ω·m corresponded exactly to the brine intrusion zone. The evolution of the freshwater-saltwater interface unfolded in three stages: Initially, the density difference (0.025 g/cm³) dominated, with the saltwater intrusion depth at the aquifer base reaching 0.45 m, significantly exceeding the 0.04 m penetration at the upper section. During the intermediate stage, the interface morphology differentiated into an “upper triangular, lower arc-shaped” configuration. The bottom intrusion distance increased to 1.65 m, and the thickness of the brackish-freshwater mixing zone expanded from 0.1 m to 0.3 m. In the final stage, the interface stabilized and began intruding toward the surface, establishing a new hydrodynamic equilibrium. In addition, the migration rate of saline water at the aquifer base gradually decreased from 6.25 × 10⁻⁴ cm/s initially to 1.16 × 10⁻⁵ cm/s at steady state. These results reflect the dynamic coupling process between seepage and dispersion and demonstrate that this method enables effective real-time monitoring of seawater intrusion development and conditions, as well as early warning capabilities. Full article

Wind represents a pervasive yet mechanistically distinct environmental factor that reshapes species interactions primarily through habitat compression—reducing effective habitat area via behavioral avoidance, rather than altering resource availability as seen in temperatureor rainfall-driven models. This study introduces a a novel wind-modified Lotka–Volterra competition model that advances existing disturbance-dependent frameworks through two key innovations: (1) a wind-speed-dependent carrying capacity, formally expressed as the initial carrying capacity divided by a linear function of wind speed and species-specific wind sensitivity, which explicitly quantifies wind-induced habitat contraction as a nonlinear function of wind exposure; and (2) a species-specific wind sensitivity coefficient that can be experimentally calibrated. Through a rigorous stability analysis and numerical simulations, we demonstrate how wind speed modulates competitive outcomes by altering equilibrium densities and stability. Our results reveal: (a) wind can reverse competitive dominance, disproportionately excluding species with higher wind sensitivity coefficients; (b) critical wind speed thresholds exist, beyond which populations collapse due to mechanisms akin to Allee effects and demographic stochasticity; and (c) wind nonlinearly regulates coexistence, with moderate speeds sometimes stabilizing it and extreme speeds driving effective extinction. This framework provides a theoretical foundation for setting conservation thresholds and assessing the ecological impacts of wind energy projects. Full article

Tin oxide thin films were deposited by the pulsed laser ablation of a metallic Sn target at different oxygen partial pressures, ranging from 10 to 40 mTorr. Langmuir plasma probe diagnostics were performed to evaluate the effect of pressure on mean kinetic energy and density of Sn ions. It was observed that the mean kinetic energy decreased from 34 to 11 eV while the ion density decreased from 10 to 1.5 × 10¹³ cm⁻³ with increasing pressure. The films exhibited enhanced optical transmittance, increasing from 10% for the sample grown at 10 mTorr to 70% for the film deposited at 40 mTorr. Furthermore, higher deposition pressures led to wider band gap values, increasing from 1.6 to 3.9 eV for direct transitions and from 2.2 to 3.2 eV for indirect transitions with increasing oxygen pressure. These trends are consistent with progressive oxidation and partial transparency characteristic of semiconducting tin oxides. Structural characterization, based on X-ray diffraction, revealed predominantly metallic Sn diffraction peaks across the entire oxygen pressure range. However, despite this structural signature, the films exhibited optical and electronic properties characteristic of tin oxides. This apparent discrepancy suggests the coexistence of metallic nanoparticles embedded within an amorphous or nanocrystalline SnO₂/SnO_x matrix. These findings provide insights into the non-equilibrium oxidation dynamics of tin and the formation of metastable SnO_x phases during pulsed laser deposition. Full article