Search Results (850)

This study introduces a novel analytical framework for investigating the vibration characteristics of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) elliptical cylindrical shells under arbitrary boundary conditions. Unlike previous studies that focused on simplified geometries or specific boundary conditions, this work combines the least-squares weighted residual method (LSWRM) with an adapted variational principle, addressing high-order vibration errors and ensuring continuity across structural segments. The material properties are modeled using an extended rule of mixtures, capturing the effects of carbon nanotube volume fractions and distribution types on structural dynamics. Additionally, virtual boundary techniques are employed to generalize elastic boundary conditions, enabling the analysis of complex boundary-constrained structures. Numerical validation against existing methods confirms the high accuracy of the proposed framework. Furthermore, the influence of geometric parameters, material characteristics, and boundary stiffness on vibration behavior is comprehensively explored, offering a robust and versatile tool for designing advanced FG-CNTRC structures. This innovative approach provides significant insights into the optimization of nanoscale reinforced composites, making it a valuable reference for engineers and researchers in aerospace, marine, and construction industries. Full article

Background: Contrast-enhanced mammography (CEM) has recently gained recognition as an effective alternative to breast magnetic resonance imaging (MRI) for assessing breast lesions, offering both morphological and functional imaging capabilities. However, the phenomenon of background parenchymal enhancement (BPE) remains a critical consideration, as it can affect the interpretation of images by obscuring or mimicking lesions. While the impact of BPE has been well-documented in MRI, limited data are available regarding the factors influencing BPE in CEM and its relationship with breast cancer (BC) characteristics. Materials: This retrospective study included 116 patients with confirmed invasive BC who underwent CEM prior to biopsy and surgery. Data collected included patient age, breast density, receptor status, tumor grading, and the Ki-67 proliferation index. BPE was evaluated by two radiologists using the 2022 ACR BI-RADS lexicon for CEM. Statistical analyses were conducted to assess the relationship between BPE, patient demographics, and tumor characteristics. Results: The study found a significant association between higher levels of BPE and specific patient characteristics. In particular, increased BPE was more commonly observed in patients with higher breast density (p < 0.001) and those who were pre-menopausal (p = 0.029). Among patients categorized under density level B, the majority exhibited minimal BPE, while those in categories C and D showed progressively higher levels of BPE, indicating a clear trend correlating higher breast density with increased enhancement. Additionally, pre-menopausal patients demonstrated a higher likelihood of moderate to marked BPE compared to post-menopausal patients. Despite these significant associations, the analysis did not reveal a meaningful correlation between BPE intensity and tumor subtypes (p = 0.77) or tumor grade (p = 0.73). The inter-reader agreement for BPE assessment was substantial, as indicated by a weighted kappa of 0.78 (95% CI: 0.68–0.89), demonstrating consistent evaluation between radiologists. Conclusions: These findings suggest that BPE in CEM is influenced by factors like breast density and age, aligning with patterns observed in MRI studies. However, BPE intensity was not associated with tumor subtypes or grades, indicating a poorer prognosis. These insights highlight the potential of BPE as a risk biomarker in preventive follow-up, particularly for patients with high breast density and pre-menopausal status. Further multicentric and prospective studies are needed to validate these results and deepen the understanding of BPE’s role in CEM diagnostics. Full article

Background and Objectives: According to the International Working Group on Diabetic Foot (IWGDF) risk classification, the estimated risk of developing a diabetic foot ulcer (DFU) is much higher in patients with a history of DFUs (Grade 3) compared to those with a peripheral neuropathy but without a history of DFUs (Grades 1 and 2). It has been suggested that microcirculation impairment is involved in DFU genesis and could be taken into account to refine the existing risk classification. The aim of this study was to evaluate microcirculation parameters in patients with diabetes according to their estimated DFU risk. Materials and Methods: A total of 172 patients with type 2 diabetes associated with a peripheral neuropathy and/or a history of DFUs were included and classified into two groups (Grade 1–2 and Grade 3) according to the IWGDF classification. All patients underwent an evaluation of peripheral neuropathy, plantar sudomotor function, and skin microcirculation parameters. These different parameters were compared between both groups. Results: There was no significant difference between the two groups in terms of age, diabetes duration, transcutaneous oxygen pressure level, skin microcirculatory reactivity, neuropathy disability score, neuropathy symptom score, or thermal sensitivity. Patients in Grade 3 were more likely to present with retinopathy (OR 3.15, 95%CI [1.53; 6.49]) and severe sudomotor dysfunction (OR 2.73 95%CI [1.29; 5.80] but less likely to have abnormal VPT (OR 0.20 95%CI [0.05; 0.80]). Conclusions: The present study found more retinopathy and a more pronounced alteration to sudomotor function in Grade 3 patients, suggesting that these parameters could be considered to better identify patients at high risk of DFUs. Full article

The most commonly used methods to chemically assess grape and wine quality with high sensitivity and selectivity require lengthy analysis time and can be resource intensive. Here, we developed a rapid and non-destructive method that would help in grading and decision support. In this work, we demonstrate that integrating a three-dimensional (3D) material for volatile sampling with mass spectrometry detection can be used to sample grapes for phytosanitary, quality or smoke-taint assessments at low levels of marker compounds. An efficient zeolitic imidazolate framework-8 (ZIF-8) material was synthesised in situ on nickel foam (NF), taking advantage of its ultrahigh surface area, structural diversity, and functionality as an emerging nanostructured material for preconcentrating low-level wine and grape quality-related volatiles. When used as a sorbent in thermal desorption tubes and coupled directly to active capillary mass spectrometry, the average signal across the selected analytes increased by ~50% as compared to Tenax TA, a commercially available polymer, in a measurement that takes less than two minutes. The first integration of 3D materials into mass spectrometry opens new possibilities for developing new material architecture with enhanced selectivity of next-generation multifunctional instrumentation for volatile analysis and product quality assessment. Full article

An analytical solution is presented for axisymmetric free vibration analysis of a functionally graded piezoelectric circular plate on the basis of the three-dimensional elastic theory of piezoelectric materials. The material properties are assumed to follow an exponential law distribution through the thickness of the circular plate. The state space equations for the free vibration behavior of the functionally graded piezoelectric circular plate are developed based on the state space method. The finite Hankel transform is utilized to obtain an ordinary differential equation with variable coefficients. By virtue of the proposed exponential law model, we have ordinary differential equations with constant coefficients. Then, the free vibration behaviors of the functionally graded piezoelectric circular plate with two kinds of boundary conditions are investigated. Some numerical examples are given to validate the accuracy and stability of the present model. The influences of the exponential factor and thickness-to-span ratio on the natural frequency of the functionally graded piezoelectric circular plate, constrained by different boundary conditions, are discussed in detail. Full article

The aim of the present work is to study the atmospheric corrosion behavior of metals exposed to both urban (Milan, IT-Lombardia) and marine (Bonassola, IT-Liguria) atmospheres in Italy. A number of coupons (100 × 150 mm) of carbon steel (CS), hot-dip galvanized steel (GS) and different grades of stainless steel (SS) were exposed. At fixed periods of time, samples were characterized by means of Linear Polarization Resistance (LPR), mass loss tests and corrosion product analysis. The corrosion rate on carbon steel exposed to an urban atmosphere, obtained by means of mass loss tests and LPR, are in good agreement with the value estimated by the dose–response function according to the ISO 9223 standard. The yielded results can be classified in corrosivity class C2 of the same ISO 9223. Similar measurements on galvanized steel exhibited a coherent average corrosion rate. Higher corrosion rates were measured for samples exposed to a marine atmosphere for both materials, with values belonging to exposure classes C4-C5 for both materials. Stainless steel samples exhibited only superficial staining in the case of marine exposure, even after just a few months. Full article

The research examines the impact of nonlinear energy sinks (NES) on the reduction in the nonlinear vibratory responses of eccentrically stiffened functionally graded (ESFG) panels exposed to hydrodynamic loads. To simulate real marine environments, hydrodynamic forces, such as lift and drag that change with velocity, have already been determined experimentally using Matveev’s equations for a particular ship. The material composition of both the panel and the stiffeners varies across their thickness. The stiffeners are modeled using Lekhnitskii’s smeared stiffener approach. Additionally, analytical approaches implement the classical shell theory (CST) with considerations for geometric nonlinearity, along with the Galerkin method for calculations. The P-T method is subsequently employed to determine the nonlinear vibratory behavior of ESFG panels. In this method, the piecewise constant argument is used jointly with the Taylor series expansion, which is why it is named the P-T method. The findings reveal that NES can effectively dissipate vibrational energy, contributing to the extended service life of marine structures while reducing the need for frequent maintenance. This study supports sustainability objectives by increasing energy efficiency, lessening structural fatigue, and improving the overall environmental impact of marine vessels and infrastructure. Full article

Bone transplantation ranks second worldwide among tissue prosthesis surgeries. Currently, one of the most promising approaches is regenerative medicine, which involves tissue engineering based on polymer scaffolds with biodegradable properties. Once implanted, scaffolds interact directly with the surrounding tissues and in a fairly aggressive environment, which causes biodegradation of the scaffold material. The aim of this work is to experimentally investigate the changes in the effective mechanical properties of polylactide scaffolds manufactured using additive technologies. The mechanism and the rate of the degradation process depend on the chosen material, contact area, microstructural features, and overall architecture of sample. To assess the influence of each of these factors, solid samples with different dimensions and layers orientation as well as prototypes of functionally graded scaffolds were studied. The research methodology includes the assessment of changes in the mechanical properties of the samples, as well as their structural characteristics. Changes in the mechanical properties were measured in compression tests. Microcomputed tomography (micro-CT) studies were conducted to evaluate changes in the microstructure of scaffold prototypes. Changes caused by surface erosion and their impact on degradation were assessed using morphometric analysis. Nonlinear changes in mechanical properties were observed for both solid samples and lattice graded scaffold prototypes depending on the duration of immersion in NaCl solution and exposure to different temperatures. At the temperature of 37 °C, the decrease in the elastic modulus of solid specimens was no more than 16%, while for the lattice scaffolds, it was only 4%. For expedited degradation during a higher temperature of 45 °C, these ratios were 47% and 16%, respectively. The decrease in compressive strength was no more than 32% for solid specimens and 17% for scaffolds. The results of this study may be useful for the development of optimal scaffolds considering the impact of the degradation process on their structural integrity. Full article

This study advances the state of the art by computing the macroscopic elastic properties of 2D periodic functionally graded microcellular materials, incorporating both isotropic and orthotropic solid phases, as seen in additively manufactured components. This is achieved through numerical homogenization and several novel MATLAB implementations (known in this study as Cellular_Solid, Homogenize_test, homogenize_ortho, and Homogenize_test_ortho_principal). The developed codes in the current work treat each cell as a material point, compute the corresponding cell elasticity tensor using numerical homogenization, and assign it to that specific point. This is conducted based on the principle of scale separation, which is a fundamental concept in homogenization theory. Then, by deriving a fit function that maps the entire material domain, the homogenized material properties are predicted at any desired point. It is shown that this method is very capable of capturing the effects of orthotropy during the solid phase of the material and that it effectively accounts for the influence of void geometry on the macroscopic anisotropies, since the obtained elasticity tensor has different $E_1$ and $E_2$ values. Also, it is revealed that the complexity of the void patterns and the intensity of the void size changes from one cell to another can significantly affect the overall error in terms of the predicted material properties. As the stochasticity in the void sizes increases, the error also tends to increase, since it becomes more challenging to interpolate the data accurately. Therefore, utilizing advanced computational techniques, such as more sophisticated fitting methods like the Fourier series, and implementing machine learning algorithms can significantly improve the overall accuracy of the results. Furthermore, the developed codes can easily be extended to accommodate the homogenization of composite materials incorporating multiple orthotropic phases. This implementation is limited to periodic void distributions and currently supports circular, rectangular, square, and hexagonal void shapes. Full article

Plasma-facing components (PFCs) were simulated by ANSYS, and the influence of gradient layer number and composition distribution index on the distribution of temperature field and stress field was analyzed. The simulation results show that a gradient structure with four gradient layers and a component distribution index of 1 makes the PFC assembly have lower overall temperature and lower thermal stress. Tungsten–copper functionally graded materials (W–Cu FGMs) (W-20 vol% Cu/W-40 vol% Cu/W-60 vol% Cu/W-80 vol% Cu) were fabricated by a selective laser melting (SLM) process based on finite element simulation results. The effects of microstructure on the hardness, internal stresses, thermal conductivity, and thermal expansion coefficient of the W–Cu FGMs were evaluated. The results show that hardness increases from 196 to 1173 HV_0.3 with increasing W content. The internal stresses of W-20 vol% Cu, W-40 vol% Cu, W-60 vol% Cu, and W-80 vol% Cu are about 191.7 MPa, 627 MPa, 1049.5 MPa, and 561.9 MPa, respectively. The thermal conductivity of the W–Cu FGM is 23 W/m·K and the thermal diffusion coefficient is 10 mm²/s at 25 °C, and the thermal conductivity rises to 70 W/m·K and the thermal diffusion coefficient rises to 18.5 mm²/s at 800 °C. After 100 thermal shock cycles, the internal defects increased, but the interface between the gradient layers remained well bonded. Full article

This paper studies the thermomechanical low-velocity impact behaviors of geometrically imperfect nanoplatelet-reinforced composite (GRC) beams considering the von Kármán nonlinear geometric relationship. The graphene nanoplatelets (GPLs) are assumed to have a functionally graded (FG) distribution in the matrix beam along its thickness, following the X-pattern. The Halpin–Tsai model and the rule of mixture are employed to predict the effective Young modulus and other material properties. Dividing the impact process into two stages, the corresponding impact forces are calculated using the modified nonlinear Hertz contact law. The nonlinear governing equations are obtained by introducing the von Kármán nonlinear displacement–strain relationship into the first-order shear deformation theory and dispersed via the differential quadrature (DQ) method. Combining the governing equation of the impactor’s motion, they are further parametrically solved by the Newmark-β method associated with the Newton–Raphson iterative process. The influence of different types of geometrical imperfections on the nonlinear thermomechanical low-velocity impact behaviors of GRC beams with varying weight fractions of GPLs, subjected to different initial impact velocities, are studied in detail. Full article

This paper presents a method for producing VTMS/HAp/VTMS/VTMS multilayer coatings on a Grade 2 titanium substrate and characterizes their structure and functional properties. Two solutions were used to produce the coatings: one based on vinyltrimethoxysilane (VTMS) and the other on hydroxyapatite (HAp) powder. The coatings were applied using immersion using the sol-gel method. Microstructural tests of the multilayer coatings were performed, their chemical composition was determined, and the structure was characterized using Fourier Transform Infrared Spectroscopy (FTIR). A detailed analysis of the geometric structure of the coatings was carried out both before and after corrosion tests. The geometric structure of the multilayer coatings was analyzed using a light microscope and an atomic force microscope (AFM). The thickness of the coatings was determined using a Testan DT-10 AN 120 157 m, and the adhesion of the coatings to the substrate was analyzed using Scotch™ tape. The corrosion resistance of the coatings in simulated body fluid was tested to evaluate their suitability for implantology. As demonstrated by the research presented in this paper, the sol–gel process can successfully produce silane coatings by adding hydroxyapatite powder. The new materials proposed in this study can effectively protect metal materials used in medicine against corrosion. Full article

Multi-head 3D printers afford the ability to create composite structures with significant differences in properties compared to those created through traditional molding techniques. In addition to the usage of different viscoelastic polymeric materials, the selective spatial placement of the build materials enables the creation of layered and graded geometries to achieve specific mechanical and/or vibrational characteristics. This paper describes how the mechanical properties of the individual materials can be used to predict the damping and natural frequencies of a 3D-printed graded structure. Such structures can find usage in rotating machinery, beams, etc., where vibrational characteristics must be controlled. The simulation and experimental results are presented and two forms of the storage and loss modulus are considered: fixed and variable. For the latter condition, E′ and E″ are established as functions of temperature and frequency. Modal vibration testing of the graded samples shows a good match between the simulation and experimental trials, thereby supporting the proposed model as a useful tool for prescribing the structure of a printed part with tailored dynamic properties. Full article

Background and Objectives: Orthognathic surgery is used to restore a correct anatomical and functional relationship between the jaws, with postoperative nasal septal deviation (NSD) being a common complication of Le Fort I osteotomy (LF-IO). The aim of this study was to evaluate the occurrence of NSD after LF-IO and to identify possible risk factors. Materials and Methods: Pre- and postoperative cone beam computed tomography (CBCT) scans from 2018 to 2023 of 102 patients after LF-IO were analyzed. After categorizing the preoperative NSDs according to the Mladina classification, the next step was to measure the angle of deviation and classify the severity grades. Pre- and postoperative NSDs were compared using a paired Wilcoxon signed-rank test and postoperative changes in NSD were correlated with surgery-relevant characteristics by calculating Spearman’s correlation coefficients. Results: Postoperatively, an increase in NSD was observed in 62 cases and 35 patients showed a decrease. In both cases with an increase and a decrease in NSD, the preoperatively measured deviations showed a highly significant difference compared to postoperative NSDs (both p < 0.001). Age correlated significantly with increases in deviation (r = 0.28, p = 0.014, CI: −1.0–−0.068) and anterior maxillary displacement showed a significant correlation with a decrease in NSD (r = 0.296, p = 0.042, CI: 0.006–1.0). Gender, cranial and caudal movements of the maxilla had no influence on the results of the NSDs. Conclusions: LF-IO has an influence on NSD and can both intensify and attenuate it. In addition, the risk of an increase in nasal deviation after this surgical procedure rises with the patient’s age and decreases with anterior displacement of the maxilla. Full article

The enhancement of the utilization rate of solid waste, along with balancing the comprehensive performance of materials, presents a significant challenge in the development of new functional building materials. This study examined the effects of high concentrations of iron tailing powder on the crystallization characteristics, pore structure, compressive strength, and water absorption of modified magnesium oxysulfate (MOS) foam cement with different dry densities. Furthermore, employing chemical foaming technology, the study characterized and analyzed the microstructure of modified MOS foam cement hydration products through scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD). The results indicated that the addition of an acidic modifier effectively facilitated the hydration reaction in the MgO-MgSO₄-H₂O system, enhancing the micro-crystallization characteristics of MOS foam cement. The internal pores were uniformly round, with a dense crystal structure within the pore walls. The compressive strength of the material with 40% dry density A08 grade iron tailing powder reached 6.83 MPa, and the lowest water absorption was 5.32% at a dry density of A09. Full article