Search Results (151)

This research focuses on designing polymer membranes as biocompatible materials using home-built electrospinning equipment, offering alternative solutions for tissue regeneration applications. This technological development supports cell growth on biomaterial substrates, including hepatocellular carcinoma (Hep-G2) cells. This work researches the compatibility of polymer membranes (fiber mats) made of polyvinylidene difluoride (PVDF) for possible use in cellular engineering. A standard culture medium was employed to support the proliferation of Hep-G2 cells under controlled conditions (37 °C, 4.8% CO₂, and 100% relative humidity). Subsequently, after the incubation period, electrochemical impedance spectroscopy (EIS) assays were conducted in a physiological environment to characterize the electrical cellular response, providing insights into the biocompatibility of the material. Scanning electron microscopy (SEM) was employed to evaluate cell adhesion, morphology, and growth on the PVDF polymer membranes. The results suggest that PVDF polymer membranes can be successfully produced through electrospinning technology, resulting in the formation of a dipole structure, including the possible presence of a polar β-phase, contributing to piezoelectric activity. EIS measurements, based on R_ct and C_dl values, are indicators of ion charge transfer and strong electrical interactions at the membrane interface. These findings suggest a favorable environment for cell proliferation, thereby enhancing cellular interactions at the fiber interface within the electrolyte. SEM observations displayed a consistent distribution of fibers with a distinctive spherical agglomeration on the entire PVDF surface. Finally, integrating piezoelectric properties into cell culture systems provides new opportunities for investigating the influence of electrical interactions on cellular behavior through electrochemical techniques. Based on the experimental results, this electrospun polymer demonstrates great potential as a promising candidate for next-generation biomaterials, with a probable application in tissue regeneration. Full article

Dual-active bridge (DAB) converters have emerged as a preferred topology in electric vehicle charging and energy storage applications, owing to their structurally symmetric configuration and intrinsic galvanic isolation capabilities. However, conventional triple-phase shift (TPS) control strategies face significant challenges in maintaining high efficiency across ultra-wide output voltage and load ranges. To exploit the inherent structural symmetry of the DAB topology, a symmetric optimization strategy based on triple-phase shift (SOS-TPS) is proposed. The method specifically targets the forward buck operating mode, where an optimization framework is established to minimize the root mean square (RMS) current of the inductor, thereby addressing both switching and conduction losses. The formulation explicitly incorporates zero-voltage switching (ZVS) constraints and operating mode conditions. By employing the Karush–Kuhn–Tucker (KKT) conditions in conjunction with the Lagrange multiplier method (LMM), the refined control trajectories corresponding to various power levels are analytically derived, enabling efficient modulation across the entire operating range. In the medium-power region, full-switch ZVS is inherently satisfied. In the low-power operation, full-switch ZVS is achieved by introducing a modulation factor λ, and a selection principle for λ is established. For high-power operation, the strategy transitions to a conventional single-phase shift (SPS) modulation. Furthermore, by exploiting the inherent symmetry of the DAB topology, the proposed method reveals the symmetric property of modulation control. The modulation strategy for the forward boost mode can be efficiently derived through a duty cycle and voltage gain mapping, eliminating the need for re-derivation. To validate the effectiveness of the proposed SOS-TPS strategy, a 2.3 kW experimental prototype was developed. The measured results demonstrate that the method ensures ZVS for all switches under the full load range, supports ultra-wide voltage conversion capability, substantially suppresses RMS current, and achieves a maximum efficiency of 97.3%. Full article

This study addresses the limitations of conventional evaluation methods caused by low porosity, strong heterogeneity, and complex pore structures in tight sandstone reservoirs. Through integrated rock physics experiments and multi-physical field modeling, the research systematically investigates the coupled response mechanisms between electrical and elastic parameters. The experimental approach includes pore structure characterization, quantitative mineral composition analysis, resistivity and polarizability measurements under various saturation conditions, P- and S-wave velocity testing, and scanning electron microscopy (SEM) imaging. The key findings show that increasing porosity leads to significant reductions in resistivity and elastic wave velocities, while also increasing surface conductivity. Specifically, clay minerals enhance surface conductivity through interfacial polarization effects and decrease rock stiffness, which exacerbates wave velocity attenuation. Furthermore, resistivity exhibits a nonlinear negative correlation with water saturation, with sharp increases at low saturation levels due to the disruption of conductive pathways. By integrating the Modified Generalized Effective Medium Theory of Induced Polarization (MGEMTIP) and Kuster–Toksöz models, this study establishes quantitative relationships between porosity, saturation, and electrical/elastic parameters, and constructs cross-plot templates that correlate elastic wave velocities with resistivity and surface conductivity. These analyses reveal that high-porosity, high-saturation zones are characterized by lower resistivity and wave velocities, coupled with significantly higher surface conductivity. The proposed methodology significantly improves the accuracy of reservoir evaluation and enhances fluid identification capabilities, providing a solid theoretical foundation for the efficient exploration and development of tight sandstone reservoirs. Full article

To evaluate the ecological remediation effect of Salix matsudana × alba on saline coastal soils, we established a five-year field experiment in Rudong County, Jiangsu Province, China. The experiment was designed with three salinity gradients (low, medium, and high) and five plant spacing treatments (2 × 2 m, 2 × 3 m, 3 × 3 m, 3 × 4 m, and 4 × 4 m). Soil samples were collected annually at a depth of 0–20 cm using grid and random sampling methods. Indicators of soil physicochemical properties and heavy metal content were measured, including soil organic matter (SOM), pH, total nitrogen (TN), total phosphorus (TP), total potassium (TK), electrical conductivity (EC), total salinity (TS), and bulk density (BD). Additionally, eight heavy metals were analyzed: zinc (Zn), chromium (Cr), nickel (Ni), copper (Cu), cadmium (Cd), lead (Pb), arsenic (As), and mercury (Hg). Results showed that the hybrid willow significantly improved SOM content by up to 90% and reduced EC and TS by 52% and 60% over five years, especially under low and medium salinity conditions with dense planting (2 × 2 m, 2 × 3 m). The content of most heavy metals exhibited a decreasing trend or remained stable, indicating the plant’s phytostabilization potential (i.e., stabilization of heavy metals via plant-soil interaction). Principal component analysis (PCA) and random forest (RF) modeling identified SOM, EC, TS, and BD as the dominant factors influencing soil quality improvement. A soil quality index (SQI) was constructed based on PCA-derived weights, which further confirmed the positive ecological effect of this hybrid species on coastal saline soils. This study provides scientific evidence supporting the use of Salix matsudana × alba as a promising species for large-scale ecological restoration in coastal saline-alkaline lands. Full article

Gas extraction is the main method to reduce the gas content of a coal seam and prevent coal and gas outburst. The sealing depth is one of the key parameters affecting the sealing effect. The principle of the high-density direct current method is to lay electrodes underground, and by injecting a stable DC current into the underground medium, the potential difference is measured to calculate the apparent resistivity, which reflects the difference in electrical conductivity of the underground rock or coal body, and then inferring the physical characteristics, such as its structure, water content, or stress state. Based on the basic principle of the high-density direct current method, this study analyzed the change rule of resistivity after the secondary stress of the roadway; tested the distribution of the roadway stress field in Juji Mine; and finally, determined the sealing depth of this coal seam. The main conclusions were as follows: The resistivity of the loose crushing zone after the roadway disturbance stress corresponded to the plasticity and destruction stage of the coal body, and the resistivity was larger compared with that of the original rock stress area. The stress concentration zone corresponded to the compression stage, where the destruction of the coal and rock state was smaller, and the resistivity was smaller compared with that of the original rock stress area. The range of the loose circle of the roadway of the coal seam was 6 m, and the range of the stress concentration zone was 6–17.5 m. The range of resistivity changes of the loose crushing zone was larger, and it had a large range of resistance, which had a good effect. The resistivity of the loose broken zone varied widely and was random, while the visual resistivity of the stress concentration zone was basically the same and was stable. Full article

This study systematically investigates the mechanistic effects of multifactor interactions (including soil properties, climatic conditions, and cultivation practices) on the productivity parameters (grain yield, stover yield, dry biomass, harvest index) of maize cultivars of different maturity groups in the arid region of Xinjiang, China. Twelve representative maize-growing counties were selected as study sites, where we collected maize samples to measure HI, grain yield, stover yield, and soil physicochemical properties (e.g., organic matter content, total nitrogen, and available phosphorus). Additionally, climate data (effective accumulated temperature) and agronomic parameters (planting density) were integrated to comprehensively analyze the interactive effects of multiple environmental factors on HI using structural equation modeling (SEM). The results demonstrated significant varietal differences in HI across maturity periods. Specifically, early-maturing cultivars showed the highest average HI (0.58), significantly exceeding those of medium-maturing (0.55) and late-maturing varieties (0.54). Environmental analysis further revealed that soil phosphorus content (both available and total phosphorus), elevation, and organic matter content significantly positively affected HI, whereas soil bulk density and electrical conductivity exhibited negative impacts. Notably, HI exhibited a strong negative correlation with stover yield (R² = 0.49), but remained relatively stable across different dry matter (DM) and grain yield levels. Despite the strong positive correlation between DM and grain yield (R² = 0.81), the relative stability of HI suggests that yield improvement requires balanced optimization of both DM and partitioning efficiency. This study provides crucial theoretical foundations for optimizing high-yield maize cultivation systems, regulating fertilizer application rates and their ratios, and improving the configuration of planting density in arid regions. These findings offer practical guidance for sustainable agricultural development in similar environments. Full article

La_1−xCa_x(Co_0.25Cr_0.25Fe_0.25Ni_0.25)O_3−δ perovskite powders were prepared via a sol-gel process. The A-site was doped with calcium, while four elements—cobalt, chromium, iron, and nickel—in equiatomic amounts made up the B-site. The configurational entropy was calculated to increase with the addition of calcium from medium to high entropy. The synthesized powders were heated to 1400 °C in air for 2 h to sinter them. The effect of doping on the resulting sintered materials was observed via density measurements and electron microscopy. The electrical conductivity was measured in air as a function of temperature to 900 °C. Conductivity versus composition indicates that an increase in entropy has a marked effect on electrical conductivity, leading to two distinct relationships with temperature. Full article

In this paper, we report on the growth and characterization of high doping concentration (2.1 at%) ytterbium (Yb) doped lithium niobate (Yb:LiNbO₃) crystal. By using a slightly modified Czochralski method, we have successfully grown a usable size (2 mm × 2 mm × 30 mm) Yb:LiNbO₃ single crystal. We also conducted the energy-dispersive X-ray spectroscopy (EDS) and the X-ray diffraction (XRD) analyses, which experimentally confirm that the grown crystal is a Yb:LiNbO₃ single crystal. We also measured the absorption and emission spectra of the grown crystal. It was found out that there is a near-flat broad emission within a spectral range of 1004–1030 nm when excited at 980 nm for this high doping concentration Yb:LiNbO₃ crystal. Such a near-flat broad emission can be very useful for realizing high slope efficiency ultrafast (femtosecond) lasing in the Yb:LiNbO₃ crystal due to the low quantum defect of the Yb:LiNbO₃ crystal. We also investigated the electro-optic effect of the Yb:LiNbO₃. The experimental result confirms that the electro-optic (EO) effect of a highly doped (2.1 at%) lithium niobate crystal is close to the EO value of the pure lithium niobate. Thus, the highly doped Yb:LiNbO₃ crystal can still be an effective electrically tunable lasing medium. It can enable electrically tunable, high slope efficiency femtosecond lasing due to the combined features, including (1) a near flat broad emission spectrum at the spectral range of 1004–1030 nm, (2) a non-compromised electro-optic effect at high doping concentration Yb:LiNbO₃ crystal, and (3) a low quantum defect. Full article

Increasing the proportion of clean energy within the energy structure is a crucial strategy for achieving energy transformation. Hydrogen and ammonia, as leaders in clean energy technologies, have garnered significant global attention. The combination of hydrogen and ammonia has emerged as a novel form of energy storage, transportation, and conversion; however, the safety aspects of their application process warrant closer attention. Research on hydrogen safety has been conducted extensively, with particular focus on the leakage, diffusion, combustion, and explosion processes. Both theoretical research and engineering applications have advanced significantly. In particular, hydrogen detection technology, primarily based on electrical measurement, has matured considerably, while schlieren imaging-based flow field visualization technology is progressing steadily. In contrast, safety research concerning ammonia remains in its early stages. Research on the leakage and diffusion characteristics of ammonia predominantly focuses on liquid ammonia, with a strong emphasis on engineering applications. Studies on the combustion and explosion characteristics of ammonia primarily address flame parameters and the combustion development laws. Ammonia serves as an efficient hydrogen storage medium. The conversion process involving hydrogen and ammonia will occur simultaneously in both time and space. Current research has not adequately addressed the safety concerns associated with the application process of hydrogen–ammonia mixtures. Future research on the safety of hydrogen–ammonia application processes should focus on the diffusion characteristics and combustion and explosion behaviors, as well as the development of electrical measurement detection technologies and optical flow field visualization techniques for hydrogen–ammonia mixtures. Full article

A one-micron-thick pure zinc oxide (ZnO) and nitrogen-doped zinc oxide (N-ZnO) film were fabricated on p-type, pristine (non-porous), and porous gallium nitride (GaN) substrates using a radio frequency (RF) sputtering technique at room temperature. The doping medium was nitrogen gas, which has a flow rate that ranges from 0 to 10 sccm (0 sccm refers to pure ZnO). The photoelectrochemical etching process, using ultraviolet light, was employed to etch the wafer surface and create a porous GaN substrate. ZnO films were developed on GaN with ZnO powder as the target material under vacuum conditions. This research aimed to investigate how variations in substrate and doping influenced the structural, optical, and electrical characteristics of the resulting thin films. The SEM images indicated that the pores developed on the etched GaN surface had a spherical shape. The A₁ (LO) phonon peak at 750.2 cm⁻¹ was observed in the Raman spectrum of the etched porous GaN. The X-ray diffraction (XRD) analysis confirmed that the films grown on GaN possessed a hexagonal wurtzite structure and the observed peak shift of (101) in all N-ZnO films suggested interstitial nitrogen doping. For the N-ZnO films, the UV-visible cut-off wavelength shifted towards the blue region. The root mean square (RMS) roughness of the N-ZnO films, measured using atomic force microscopy (AFM), was found to decrease with an increasing N-doping concentration. The 10 sccm sample exhibited the lowest roughness value of 1.1 nm, whereas the pure ZnO film showed the highest roughness of 3.4 nm. The N-ZnO thin films were found to exhibit p-type conductivity, as computed by Hall measurements using the van der Pauw method, and the higher value of carrier concentration obtained for the nitrogen gas flow rate of 8 sccm was 5.29 × 10²¹ cm⁻³. Full article

Oil leakage during the processes of extraction, storage, and transportation poses a significant challenge due to the complex nature of pollution caused by frequent fluctuations in groundwater levels and variations in the water–oil interface. To effectively identify and monitor the position of the water–oil interface and displacement processes, geophysical methods have proven to be an efficient approach. This study utilizes electrical resistivity measurements to analyze changes in medium resistivity during water–oil displacement, enabling simulation of the spatial relationship between groundwater levels and petroleum contaminants based on resistivity characteristics and natural potential responses. After analysis, the following conclusions can be drawn: (1) During the water displacement process, when water forms a connected flow channel between sand and gravel, the resistivity decreases abruptly. Conversely, during oil displacement by water, when oil fills soil pores and creates a high-resistance conductive path, the resistivity increases abruptly. (2) Changes in resistivity are determined by the position of the water–oil interface. By observing characteristic changes in resistivity, it is possible to verify whether soil is undergoing water–oil displacement. (3) The direction of displacement significantly affects changes in resistivity for all three media involved due to gravity effects during water displacement by the oil process. (4) Resistance values during the water–oil displacement process are directly influenced by the size of sand particles used in experiments. Full article

Due to their biocompatibility and non-toxicity, biopolymer-based films hold significant importance in bioengineering. It is imperative to comprehend the influence of chitosan molecular weight and filler materials nature on the crystalline structure and their subsequent effect on film properties. The aim of this research was to determine how carbon nanotubes embedded within chitosan can significantly improve the performance of biopolymer-based films produced by the solvent-casting technique. Four probe measurements demonstrated that films of medium-molecular-weight chitosan/carbon nanotubes displayed an electrical conductivity value of 0.0132 S cm⁻¹, resulting in films with a low sheet resistance value of 0.0156 mΩ/Υ. Based on XRD findings, it has been demonstrated that films containing carbon nanotubes have shifted the (002) plane of chitosan towards higher angles, favoring chitosan crystal form II, which could be responsible for the enhanced mechanical performance. Structural characteristics, such as lattice strain (e), grain size (D), and dislocation density, have been calculated using the Williamson–Hall method, in which the medium-molecular-weight chitosan/CNTs film samples displayed the best crystalline quality. SEM images revealed nanotube diameters ranging in size from 140 to 300 nm, suggesting that the chitosan was effectively wrapped along carbon nanotubes. Our results indicate that developing chitosan-wrapped carbon nanotube films introduces them as potential materials for bioengineering and biomedical research. Full article

Background: Although previous studies have suggested a variety of sociodemographic and psychological factors as predictors of poor outcomes in patients with chronic low back pain (CLBP), longitudinal studies remain rare. Objectives: To examine the prognostic indicators for poor outcome at 6 months on pain, disability, quality of life, anxiety, depression and somatic symptom disorders (SSDs) in Greek backache patients and to evaluate the medium-term effects of a conservative physiotherapeutic approach (massage, ultrasound, transcutaneous electrical nerve stimulation, low-level laser and exercise program). Methods: A prospective cohort study of 145 volunteers receiving treatment for CLBP in a physiotherapy unit was conducted using random systematic sampling. The intervention was assessed by comparing pre-treatment, post-treatment and six-month measurements with Friedman’s test and the Bonferroni correction, using the pain numerical rating scale (PNRS), Roland–Morris disability questionnaire (RMDQ), EuroQol-5-dimension-5-level (EQ-5D-5L), Hospital Anxiety and Depression Scale (HADS) and Somatic Symptom Scale-8 (SSS-8). Multiple linear regression analysis was carried out to determine the impact of demographics and pre-treatment scores with scores at six months. Results: The mean age was 60.6 years (±14.7). Post-treatment, statistically significant improvements were observed across all outcome measures, including PNRS, RMDQ, EQ-5D-5L and SSS-8 (all p ≤ 0.001), with anxiety showing a notable reduction (p = 0.002). After examining the multiple regression analysis, pre-treatment SSS-8 emerged as a predictor of elevated levels of pain, disability, anxiety and depression at 6 months. Conclusions: The findings yielded not only somatic symptom burden, greater age and pain intensity as prognostic indicators for poor outcomes at six months, but also reported favorable medium-term effects for a conventional physiotherapy regimen in CLBP management, as well. Full article

This paper represents a comparative study of two rivers, namely, the Andarax River, Spain, and the River Liffey, Ireland, considering different climatic conditions and human activities and their influences on most water quality parameters. Water samples collected from different sampling sites along each river were analysed for field parameters such as the pH, dissolved oxygen (DO), total dissolved solids (TDS), electrical conductivity (EC), and nitrates, phosphates, and potassium (NPK) levels of floodplain soil. Spatial changes were assessed using various geostatistical methods such as the Pearson correlation, multiple linear regression (MLR), and water quality index (WQI). The Andarax River had a higher TDS and was turbidly higher with EC due to agricultural activities and the naturally higher evaporation in the semiarid climate. In contrast, DO levels varied widely in the River Liffey, especially in reaches under the influence of urbanisation and agricultural runoff. The artificial surface and agriculture are the strongest negative determinants of water quality in both rivers, with artificial surfaces contributing about 35.72% to the DO variation. The WQI identified the water quality in the Andarax River as poor to very poor in certain locations, while the River Liffey exhibited a good to medium quality overall, although with localised degradation in areas of high human activity. The results of this study are important for developing targeted remedial measures in diversified climate conditions and a customised water sustainability plan to address the challenges of each area. Full article

The primary aim of this study was to evaluate the spatial and temporal variation in human exposure to electromagnetic fields across different frequency bands within an urban area identified as the commercial zone of a medium-sized city. Central to this investigation was the use of an exposimeter, strategically positioned on the back of the operator and secured to the hip area via a belt, to ensure comprehensive and accurate field measurements. An initial analysis was conducted to determine the shielding coefficients of the human body, allowing for precise corrections of the electric field values used in the spatial assessment. To map power density across the study area for each frequency, kriging interpolation was applied. Furthermore, temporal variations in exposure levels were analyzed at three distinct times of day—morning business hours, afternoon business hours, and non-business hours—using robust statistical methods. The study’s innovative approach lies in the integration of GIS technology to uncover and visualize temporal patterns in exposure, particularly during periods of higher pedestrian density. This integration facilitated both the detection of temporal variations and the spatial representation of these changes, enabling rapid identification and assessment of exposure hotspots. Full article