Search Results (940)

Aluminum doping can improve the phase stability of metastable compound Sm₂Fe₁₇C_x with a high carbon content (x > 1.5). We investigated the preferential site substitution of Al, chemical bonding, and structural stability in Sm₂(Fe,Al)₁₇C₃ using first-principle calculations. Our results reveal a strong correlation between the preferential substitution of Fe by Al and the atomic site chemical environment, which affects the overall phase stability. Specifically, Al preferentially occupies the 9d site in Sm₂(Fe,Al)₁₇C₃. At the same time, Al prefers the site 6c in its parent phase Sm₂(Fe,Al)₁₇. Partial replacement of Fe with Al leads to a more negative formation energy, indicating enhanced thermodynamic stability. Crystal Orbital Hamilton Population (COHP) and Crystal Orbital Bond Index (COBI) analysis suggest that insertion of carbon weakens the bonding strength of Sm-Fe (18f) and Sm-Fe (18h), resulting in metastability of Sm₂Fe₁₇C_x. Doping Al strengthens Al-Fe, Al-Sm, Sm-Fe (18f, 18h) and Fe–C bonding in Sm₂(Fe,Al)₁₇C₃, as revealed by calculated COHP and COBI. These effects contribute to improved phase stability in the Al-doped 2:17 interstitial compound. Full article

Global navigation satellite system (GNSS) differential code bias (DCB) and topside ionosphere vertical electron content (VEC) can be estimated using onboard data from low-earth-orbit (LEO) satellites. These satellites provide the potential to make up for the lack of ground-based stations in the oceanic and polar regions and establish a high-precision global ionosphere model. In order to study the influences of different LEO-topside VEC processing methods on estimates, we creatively analyzed and compared the results and accuracy of the DCBs and LEO-topside VEC estimates using two topside VEC solutions—the SH-topside VEC (spherical harmonic-topside vertical electron content) and EP-topside VEC (epoch parameter-topside vertical electron content) methods. Some conclusions are drawn as follows. (1) Using GRACE-A data (400 km in 2016), the monthly stabilities (STDs) of GPS satellite DCBs and LEO receiver DCBs using the EP-topside VEC method are better than those using the SH-topside VEC method. For JASON-2 data (1350 km), the STD results of GPS DCBs using the SH-topside VEC method are slightly superior to those using the EP-topside VEC method, and LEO DCBs using the two methods have similar STD results. However, the root mean square (RMS) results for GPS DCBs using the SH-topside VEC model relative to the Center for Orbit Determination in Europe (CODE) products are slightly superior to those using the EP-topside VEC method. (2) The peak ranges of the actual GRACE-A-topside VEC results using the SH-topside VEC and EP-topside VEC methods are within 42 and 35 TECU, respectively, while the peak ranges of the JASON-2-topside VEC results are both within 6 TECU. Additionally, only the SH-topside VEC model results are displayed due to the EP-topside VEC method not modeling VEC. Due to the difference in orbital altitude, the results and distributions of the GRACE-topside VECs differ from those of the JASON-topside VECs, with the former being more consistent with the ground-based results, indicating that there may be different height structures in the LEO-topside VECs. In addition, we applied the IRI-GIM (International Reference Ionosphere model–Global Ionosphere Map) method to compare the LEO-based topside VEC results, which indicate that the accuracy of GRACE-A-topside VEC using the EP-topside VEC method is better than that using the SH-topside VEC method, whereas for JASON-2, the two methods have similar accuracy. Meanwhile, we note that the temporal and spatial resolutions of the SH-topside VEC method are higher than those of the EP-topside VEC method, and the former has a wide range of usability and predictive characteristics. The latter seems to correspond to the single-epoch VEC mean of the former to some extent. Full article

GNSS Precise Point Positioning (PPP) technology has been applied to the time transfer for a long time, enabling time synchronization between two arbitrary stations on a global scale. Over the past decade, Low Earth Orbit (LEO) satellite constellations have been developed to enhance GNSS, offering rapid geometry configuration variations that can accelerate PPP convergence and enhance the time link performance. In this contribution, LEO observations are integrated into GNSS to enhance the real-time PPP time transfer. Simulated LEO constellations with varying numbers of satellites are used to assess their impact on real-time PPP time transfer performance. One week of observation data from 11 globally distributed stations is used to generate 10 time links, and five experimental schemes are designed: (1) GPS/BDS-3/Galileo solution (GCE), (2) GCE with 120 LEO satellites (GCE+120L), (3) GCE with 180 LEO satellites (GCE+180L), (4) GCE with 240 LEO satellites (GCE+240L), and (5) GCE with 300 LEO satellites (GCE+300L). Results showed that compared to the GCE solution, integrating 120, 180, 240, and 300 LEO satellites increases the average number of observed satellites from 23.4 to 30.6, 34.1, 37.7, and 41.3, respectively, while reducing Time Dilution of Precision (TDOP) values from 0.547 to 0.424, 0.391, 0.363, and 0.342, respectively. Using 30 s observations, the average convergence time to STD of time link errors better than 0.1 ns is reduced from 7.95 to 5.94, 4.83, 4.46, and 4.45 min in static mode, with improvements of 25.3%, 39.2%, 43.9%, and 44.0%, respectively, and from 8.75 to 6.18, 5.17, 4.89, and 4.72 min in kinematic mode, with improvements of 29.3%, 40.8%, 44.1%, and 46.0%, respectively. Using 1 s observations, Scenarios GCE+120L, GCE+180L, GCE+240L, and GCE+300L can achieve 1 ns convergence within 1 min. The time link precision was also found to be significantly improved, i.e., from 0.337 to 0.243 ns in static mode with improvements of 27.9%, and from 0.377 to 0.253 ns in kinematic mode with improvements of 32.9%. The time link stability is significantly enhanced for averaging times between 60 and 20,000 s in both static and kinematic modes, with a maximum improvement of nearly 50%. These results have demonstrated that integrating LEO satellites can significantly enhance real-time PPP time transfer performance. Full article

Reclaimed coastal areas are highly susceptible to uneven subsidence caused by the consolidation of soft marine deposits, which can induce differential settlement, structural deterioration, and systemic risks to urban infrastructure. Further, engineering activities, such as construction and loadings, exacerbate subsidence, impacting infrastructure stability. Therefore, monitoring the integrity and vulnerability of linear urban infrastructure after construction on reclaimed land is critical for understanding settlement dynamics, ensuring safe and reliable operation and minimizing cascading hazards. Subsequently, in the present study, to monitor deformation of the linear infrastructure constructed over decades-old reclaimed land in Mokpo city, South Korea (where 70% of urban and port infrastructure is built on reclaimed land), we analyzed 79 Sentinel-1A SLC ascending-orbit datasets (2017–2023) using the Persistent Scatterer Interferometry (PSInSAR) technique to quantify vertical land motion (VLM). Results reveal settlement rates ranging from −12.36 to 4.44 mm/year, with an average of −1.50 mm/year across 1869 persistent scatterers located along major roads and railways. To interpret the underlying causes of this deformation, Casagrande plasticity analysis of subsurface materials revealed that deep marine clays beneath the reclaimed zones have low permeability and high compressibility, leading to slow pore-pressure dissipation and prolonged consolidation under sustained loading. This geotechnical behavior accounts for the persistent and spatially variable subsidence observed through PSInSAR. Spatial pattern analysis using Anselin Local Moran’s I further identified statistically significant clusters and outliers of VLM, delineating critical infrastructure segments where concentrated settlement poses heightened risks to transportation stability. A hyperbolic settlement model was also applied to anticipate nonlinear consolidation trends at vulnerable sites, predicting persistent subsidence through 2030. Proxy-based validation, integrating long-term groundwater variations, lithostratigraphy, effective shear-wave velocity (V_s³⁰), and geomorphological conditions, exhibited the reliability of the InSAR-derived deformation fields. The findings highlight that Mokpo’s decades-old reclamation fills remain geotechnically unstable, highlighting the urgent need for proactive monitoring, targeted soil improvement, structural reinforcement, and integrated InSAR-GNSS monitoring frameworks to ensure the structural integrity of road and railway infrastructure and to support sustainable urban development in reclaimed coastal cities worldwide. Full article

A star tracker lens works in the environment with the temperatures ranging from −40 °C to 80 °C (a range of 120 °C), which makes athermalization a crucial step in the design. Traditional approaches could spend quite an amount of iterative process in between the optimization for nominal condition and athermalization. It is highly desired that the optimization can start with a thermally robust layout to improve the design efficiency. This study takes the star tracker lens module with seven elements as the base for investigating the possible layout variation on dioptric power distribution and thermo-optic coefficient $dn/dT$ of the material, which are the two major factors of the layout interacting with each other to influence the thermal stability of the overall lens module. All the possible layouts are optimized firstly for the nominal condition at T = 20 °C, and only those meeting the optical performance specifications are selected for thermal performance evaluation. A merit function based on a thin lens model which represents the focal plane drift over a temperature range of 120 °C is then used as the criteria for ranking the layout variations passing the first stage. The layouts at top ranking exhibiting low focal plane drift become potential candidates as the final solution. The proposed methodology provides an efficient approach for designing thermally resilient star tracker optics, especially addressing the harsh thermal conditions encountered in Low Earth Orbit missions. Full article

This paper analyzes a discrete-time single-server retrial queue with preemptive service, Bernoulli arrivals, and adaptive retrial times, tailored to telecommunications systems. In call centers, the model captures caller retries and priority interruptions, while in cellular networks, it represents user channel access attempts with preemption for emergency calls. Using a Markov chain framework, we derive the stationary distribution, establish a stability condition, and compute performance metrics, including the mean number of retrying callers or users and orbit size probabilities. The model incorporates a novel retrial time adaptation probability, reflecting dynamic retry behaviors in telecommunications. Numerical results demonstrate the impact of arrival rates, preemption probabilities, and retrial adaptations on system performance, offering insights for optimizing call center staffing and cellular network protocols. Applications to slotted ALOHA and TDMA systems highlight the model’s practical relevance. Full article

Considering the relevance of hydrogen bonds and other intermolecular interactions in regulating the activity of the tyrosine kinase class of enzymes, an in-depth electronic structure study of these forces in the context of the BCR-ABL protein was performed through full optimizations using the ONIOM method. Rebastinib and ponatinib were docked to the target enzyme using AutoDock Vina to provide starting-point geometries, which were then optimized through ONIOM calculations. This study evaluated Frontier Molecular Orbitals (FMOs) and Bond-Critical Points (BCPs) located in the sites of interactions formed with accessible residues, such as Glu286, Met318, and Asp381. Ponatinib’s ONIOM-optimized structure was shown to not only form and preserve prominent interactions, which were shown to be significantly stronger than those formed by rebastinib, but also to be associated with a significant increase in the HOMO (Highest Occupied Molecular Orbital)−LUMO (Lowest Unoccupied Molecular Orbital) gap, indicating its potential to hinder catalytic activity by providing higher chemical stability when compared to rebastinib. Full article

Viologens are promising candidates for next-generation electrochromic devices due to their reversible color changes, low operating voltages, and structural tunability. However, their practical performance is often constrained by limited color range, stability issues, and poor charge delocalization. In this study, we present a detailed density functional theory (DFT) and time-dependent DFT (TD-DFT) investigation of asymmetric viologens based on the Benzyl-4,4′-dipyridyl-R (BnV-R) framework. A series of electron-donating and electron-withdrawing substituents (CN, COOH, PO₃H₂, CH₃, OH, NH₂) were introduced via either benzyl or phenyl linkers. Geometry optimizations for neutral, radical cationic, and dicationic states were performed at the CAM-B3LYP/6-31+G(d,p) level with C-PCM solvent modeling. Electronic structure, frontier orbital distributions, and redox potentials were correlated with substituent type and linkage mode. Natural Bond Orbital analysis showed that electron-withdrawing groups stabilize reduced states, while electron-donating groups enhance intramolecular charge transfer and switching kinetics. TD-DFT calculations revealed significant bathochromic and hyperchromic shifts dependent on substitution patterns, with phenyl linkers promoting extended conjugation and benzyl spacers minimizing aggregation. Radical cation stability, quantified via ΔE_red and comproportionation constants, highlighted cyano- and amine-substituted systems as particularly promising. These insights provide predictive design guidelines for tuning optical contrast, coloration efficiency, and electrochemical durability in advanced electrochromic applications. Full article

In this study, core–shell Ln₂O₃@carbon nanoparticles (core = Ln₂O₃ and shell = carbon; Ln = Tb and Ho) were synthesized for the first time by preparing Ln₂O₃ nanoparticles through a polyol method, followed by carbon coating using D-glucose as a carbon precursor in aqueous media. The synthesized Ln₂O₃@carbon nanoparticles exhibited good colloidal stability in solution and very low toxicity in in vitro cellular cytotoxicity tests. They exhibited paramagnetic magnetization values that increased with increasing applied field strength, resulting from spin–orbit magnetic moments of 4f-electrons; hence, they yielded negligible r₁ (<0.1 s⁻¹mM⁻¹) and appreciable r₂ values (3.446 and 3.677 s⁻¹mM⁻¹ for Ln = Tb and Ho, respectively) at 3 T, highlighting their potential as T₂ MRI contrast agents, particularly at high MR fields. In addition, the carbon coating shell exhibited photoluminescence at 460 nm, suitable for applications in fluorescence imaging probes. Full article

Pipelines and power cables are critical infrastructures in coastal areas for transporting energy resources from offshore renewable installations to onshore grids. It is important to investigate the hydrodynamic forces on pipelines and cables and their surrounding flow fields, which are highly related to their on-bottom stability. The time-varying hydrodynamic forces coefficients and unsteady surrounding flows of a near-seabed pipeline subjected to a wave-induced oscillatory boundary layer flow are studied through numerical simulations. The Keulegan–Carpenter numbers of the oscillatory flow are up to 400, which are defined based on the maximum undisturbed near-bed orbital velocity, the pipeline diameter and the period of the oscillatory flow. The investigated Reynolds number is set to $1\times {10}^4$, defined based on $U_w$ and $D$. The influences of different seabed roughness ratios $k_s/D$ (where $k_s$ is the Nikuradse equivalent sand roughness) up to 0.1 on the hydrodynamic forces and the flow fields are considered. Both a wall-mounted pipeline with no gap ratio to the bottom wall and a pipeline with different gap ratios to the wall are investigated. The correlations between the hydrodynamic forces and the surrounding flow patterns at different time steps during one wave cylinder are analyzed by using the force partitioning method and are discussed in detail. It is found that there are influences of the increasing $k_s/D$ on the force coefficients at large $\mathrm{K}\mathrm{C},$ while for the small $\mathrm{K}\mathrm{C}$, the inertial effect from the oscillatory flow dominates the force coefficients with small influences from different $k_s/D$. The FPM analysis shows that the elongated shear layers from the top of the cylinder contribute to the peak values of the drag force coefficients. Full article

Building off previous work on π-extended nickel thiophenedithiolenes, a series of thiazole-fused nickel dithiolene complexes have been prepared via similar synthetic methods, thus allowing for the addition of aryl groups to the terminal α-position of the fused thiazoledithiolene unit. In addition to π-extended complexes incorporating thiophene, phenyl, and furan end-groups, the methyl-terminated species has also been prepared as a representative of the simple nickel thiazoledithiolene core. The optical, electronic, and structural properties of these complexes have been characterized, and comparisons to the analogous nickel thiophenedithiolenes show that the replacement of thiophene by thiazole stabilizes the frontier orbitals of the thiazole-based complexes, while preserving the planar geometry, electronic delocalization, and low-energy NIR absorption of the previous nickel thiophenedithiolene species. Full article

The importance of purple corn (Zea mays L.) varieties has increased due to their high anthocyanin contents both in the kernels and the degrained cob. The aim of this work was to separate anthocyanins from degrained purple-corn cobs to assess their pigmentation potential in food matrices. Two populations of purple corn were used, namely, Negro de Ixtenco (NIX) and Negro de Ixtenco x Negro de Perú (PIX), collected in Juchitepec, Mexico. Flours of degrained cob were obtained with average moisture, crude protein, ash, lipid, crude fiber, and carbohydrate contents of 7.06, 3.70, 4.48, 0.76, 37.73, and 46.27%, respectively. Aqueous biphasic systems composed of a mixture of 7.88% trisodium citrate, 2.63% citric acid, and 50.88% ethanol were applied at an atmospheric pressure of 77,993.0 Pa and 25 °C, aided by ultrasound and orbital agitation. Extracts with anthocyanin concentrations of 33.01 and 39.55 mg per gram of degrained corn cob were obtained from NIX and PIX, respectively. Pigmentation kinetics were assessed in yogurt and corn dough, which had a logarithmic tendency towards hue angles of 2.25 and 333.05°, respectively. A 60% pigmentation relative to the limit was suggested, which required 0.45 and 11.65% of the extract in yogurt and corn dough, respectively. Pigmentation stability was verified in refrigerated yogurt and in cooked corn dough. Full article

In this study, we numerically investigate the equilibrium dynamics of a rotating system consisting of two masses connected by a massless rod within the framework of the circular restricted three-body problem. The larger primary is modeled as a radiating body and the smaller as an oblate spheroid. We explore the influence of the involved parameters, i.e., mass ratio ($\mu$), force ratio (k), radiation pressure factor ($q_1$), and oblateness coefficient ($A_2$), on the number, positions, and linear stability of equilibrium points. Zero velocity curves are presented in the equatorial plane for varying values of the Jacobi constant. Up to five equilibrium points are identified of which three are collinear ($L_1$, $L_2$, $L_3$) and two are non-collinear ($L_4$, $L_5$). The positions of all equilibria shift under variations in the perturbing parameters. While the collinear points are generally unstable, $L_1$ can exhibit stability for certain combinations of $\mu$, k, and $q_1$. The non-collinear points may also be stable under specific conditions with stability zones expanding with increased parameter values. The model is applied to the irregular, elongated asteroid 951 Gaspra, for which five equilibrium points are found. Despite positional dependence on oblateness and radiation, the perturbations do not significantly affect the equilibrium points’ stability and the motion near them remains linearly unstable. The Lyapunov families of periodic orbits emanating from the collinear equilibria of this particular system are also investigated. Full article

Non-invasive glucose monitoring remains a persistent challenge in the scientific literature due to the complexity of biological samples and the limitations of traditional optical methods. Although advances have been made in the use of near-infrared (NIR) spectrophotometry, the direct application of the Lambert–Beer Law (LBL) to such systems has proven problematic, particularly due to the non-linear behavior observed in complex organic solutions. In this context, the objective of this work is to propose and validate a methodology for the determination of the extinction coefficient of glucose in blood, taking into account the limitations of the LBL and the specificities of molecular interactions. The method was optimized through an iterative process to provide consistent results over multiple replicates. Whole blood and plasma samples from two individuals were analyzed using spectrophotometry in the 700 nm to 1400 nm. The results showed that glucose has a high spectral sensitivity close to 975 nm.The extinction coefficients obtained for glucose (${\alpha }_g$) ranged from −0.0045 to −0.0053, and for insulin (${\alpha }_i$) from 0.000075 to 0.000078, with small inter-individual variations, indicating strong stability of these parameters. The non-linear behaviour observed in the relationship between absorbance, glucose and insulin concentrations might be explained by the changes imposed by both s and p orbitals of organic molecules. In order to make the LBL valid in this context, the extinction coefficients must be functions of the analyte concentrations, and the insulin concentration must also be a function of glucose. A regression model was found which allows to differentiate glucose from insulin concentration, by considering the cuvette thickness and sample absorbance at 965, 975, and 985 nm. It can also be concluded from experiments that wavelength of approximately 975 nm is more suitable for blood glucose calculation by using photometry. The final spectra are consistent with those reported in mid-infrared validation studies, suggesting that the proposed model encompasses the key aspects of glucose behavior in biological media. Full article

This work thoroughly investigated the compound 4-(2,5-Dimethoxyphenyl)-3,4-dihydrobenzo[g]chromene-2,5,10-trione (DMDCT) using molecular docking, quantum chemical analysis, and vibrational spectroscopy methodology. The medicinal chemistry group has been particularly interested in chromene and benzochromene derivatives due to their wide range of pharmacological actions, including anticancer, antibacterial, anti-inflammatory, antioxidant, antiviral, and neuroprotective capabilities. In this connection, DMDCT has been explored to evaluate its biological, electrical, and structural properties. DFT using the B3LYP functional and 6–31G basis was established to conduct theoretical computations with the Gaussian 09 program. The findings from these computations provide insight into the following topics: NBO interactions, optimal molecular geometry, Mulliken charge distribution, frontier molecular orbitals, and MEP. Second-order perturbation theory has been used to assess stabilization energies arising from donor–acceptor interactions. Furthermore, general features such as chemical hardness, softness, and electronegativity were studied. The results suggest that DMDCT has stable electronic configurations and biologically relevant active sites. This integrated experimental and theoretical study supports the potential of DMDCT as a practical scaffold for future therapeutic applications and contributes valuable information regarding its vibrational and electronic behavior. Full article