Search Results (17)

The paper reports on obtaining visually appealing images from opal matrices to artificial samples comprising regular packing of monodisperse silica globules. We show the images of iridescence, photoluminescence, and both of them simultaneously, exciting upconversion luminescence of Er³⁺ ions from BaTiO₃ xerogel/opal matrix. Opal matrix with BaTiO₃ xerogel doped with Er³⁺ and Yb³⁺ ions demonstrates upconversion luminescence under excitation with the wavelength 980 nm of the laser with the main bands ranging from 500 to 570 nm and 640–700 nm, corresponding to the transitions from the excited states ²H_11/2, ⁴S_3/2, ⁴F_9/2, ⁴I_9/2 to the ground state ⁴I_15/2 of trivalent Er ions. In our view, the synthesis of opal matrices along with the generation of luminescent xerogels doped, for example, with trivalent lanthanides, is a promising approach for obtaining colorful images, always very individual and often very attractive, bringing joy and pleasure at concerts and other show business events. Full article

This study investigates the impact of widely used mineral fillers in self-compacting concrete compositions applied in vibration-free reinforced concrete production technology, as a means of enhancing rheological characteristics and cost-effectiveness. Three distinct types of mineral fillers, including the well-studied fillers microsilica and metakaolin, as well as the lesser-explored filler Kazakhstani natural opal-chalcedony opoka, are examined in this research. In addition to the evaluation of conventional rheological and performance properties of concretes containing these fillers, the internal processes within the cement–filler matrix are analyzed. This includes X-ray phase analysis and microstructural examination of cement hydration products in combination with a superplasticizer and each of the three minerals. The findings confirm the potential for optimizing the rheological parameters of the concrete mixture by substituting up to 15% of the cement with mineral fillers, achieving optimal viscosity and workability. It is established that compositions with the addition of microsilica and metakaolin have a more homogeneous structure, mainly represented by low-basicity calcium hydrosilicates of the CSH(B) type, along with an increase in compressive strength of up to 10%. The addition of these mineral fillers to C30/35 strength class self-compacting concrete resulted in improved frost resistance up to F300, a reduction in volumetric water absorption by up to 30%, and a decrease in shrinkage deformations by 32%. The developed SCC compositions have successfully passed production testing and are recommended for implementation in the operational processes of reinforced concrete product manufacturing plants. Full article

This study presents the development of an adaptive fuzzy control strategy for double-star PMSM-PWM inverters used in ship electrical propulsion. The approach addresses the current and speed tracking challenges of double-star permanent magnet synchronous motors (DSPMSMs) in the presence of parametric uncertainties. Initially, a modeling technique employing a matrix transformation method is introduced, generating decoupled and independent star windings to eliminate inductive couplings, while maintaining model consistency and torque control. The precise DSPMSM model serves as the foundation for an unknown nonlinear backstepping controller, approximated directly using an adaptive fuzzy controller. Through the Lyapunov direct method, system stability is demonstrated. All signals in the closed-loop system are ensured to be uniformly ultimately bounded (UUB). The proposed control system aims for low tracking errors, while also mitigating the impact of parametric uncertainties. The effectiveness of the adaptive fuzzy nonlinear control system is validated through tests conducted in hardware-in-the-loop (HIL) simulations, utilizing the OPAL-RT platform, OP4510. Full article

In order to fully utilize the control degrees of freedom of a multi-three-phase-star smooth-pole permanent magnet synchronous motor (PMSM), this paper first develops a modeling approach using a new matrix transformation method. The proposed transformation produces decoupled and independent star windings, removing the inductive couplings and preserving the model and torque control’s consistency as the number of phases increases. The model, together with a new vector control scheme, is superior for studying the effect of the winding phase angle shift on motor performance. Based on a numerical simulation, this paper focuses on the quality analysis of phase currents, non-sequential currents, and torque ripple with different phase angles for double- and triple-star PMSM drives. The control of a triple-star PMSM is validated, and the behavior analysis is investigated by OPAL-RT. Full article

Integrin β4 (ITGB4) is a member of the integrin family, which plays a crucial role in mediating cell adhesion to the extracellular matrix. Recent studies have demonstrated that ITGB4 is involved in tumorigenesis and metastasis during the development of cancer. However, the role of ITGB4 in oral squamous cell carcinoma (OSCC) remains unclear. A Multiplex immunohistochemistry (OPAL™, mIHC) assay was employed to stain ITGB4, ALDH1, PD-L1, cytokeratin (CK), CD8 and PD-1 in a human OSCC tissue microarray, containing 26 normal oral epithelium samples, 21 oral epithelium dysplasia samples and 76 OSCC samples. The expression pattern and clinicopathological characteristics of ITGB4 were analyzed and compared with those of PD-1, PD-L1, ALDH1 and CD8. The correlation between subgroups of tumor cells, including ITGB4⁺PD-L1⁺ and ITGB4⁺ALDH1⁺, and subgroups of T cells, including CD8⁺ and CD8⁺PD-1⁺, was evaluated using two-tailed Pearson’s statistics. A Kaplan–Meier curve was built, and a log-rank test was performed to analyze the survival rate of different subgroups. The mIHC staining results show that ITGB4 was mostly expressed in the tumor cells, with a significant increase in the OSCC specimens compared with normal oral epithelium and oral epithelium dysplasia. The paired analysis, conducted between the OSCC tumor tissue and normal paracancer mucosa, confirmed the results. The study further revealed that ITGB4⁺PD-L1⁺ cancer cells, but not ITGB4⁺ALDH1⁺ cancer cells, were significantly associated with the infiltration of CD8⁺ T cells (positivity p = 0.005, positive number p = 0.03). Additionally, ITGB4⁺PD-L1⁺ tumor cells were positively correlated with CD8⁺PD-1⁺ T cells (positivity p = 0.02, positive number p = 0.03). Most intriguingly, the subgroup of ITGB4/PD-L1^high with CD8/PD-1^high displayed the best prognosis compared with the other considered subgroups. The results show that the expression of ITGB4 was increased in OSCC compared with normal oral mucosa. Furthermore, a specific subgroup with high levels of expression of ITGB4/PD-L1 and CD8/PD-1 was found to have a relatively better prognosis compared with the other subgroups. Ultimately, this study sheds light on the potential role of ITGB4 in OSCC and provides a basis for further investigation. Full article

SERS substrates formed by spherical silver nanoparticles (Ag-NPs) with a 15 nm average diameter adsorbed on Si substrate at three different concentrations and Ag/PMMA composites formed by an opal of PMMA microspheres of 298 nm average diameter were synthesized. The Ag-NPs were varied at three different concentrations. We have observed from SEM micrographs, in the Ag/PMMA composites, the periodicity of the PMMA opals is slightly altered as the Ag-NP concentration is increased; as a consequence of this effect, the PBGs maxima shift toward longer wavelengths, decrease in intensity, and broaden as the Ag-NP concentration is increased in the composites. The performance of single Ag-NP and Ag/PMMA composites as SERS substrates was determined using methylene blue (MB) as a probe molecule with concentrations in the range of 0.5 µM to 2.5 µM. We found that in both single Ag-NP and Ag/PMMA composites as SERS substrates, the enhancement factor (EF) increases as the Ag-NP concentration is increased. We highlight that the SERS substrate with the highest concentration of Ag-NPs has the highest EF due to the formation of metallic clusters on the surface, which generates more “hot spots”. The comparison of the EFs of the single Ag-NP with those of Ag/PMMA composite SERS substrates shows that the EFs of the former are nearly 10-fold higher than those of Ag/PMMA composites. This result is obtained probably due to the porosity of the PMMA microspheres that decreases the local electric field strength. Furthermore, PMMA exerts a shielding effect that affects the optical efficiency of Ag-NPs. Moreover, the metal–dielectric surface interaction contributes to the decrease in the EF. Other aspect to consider in our results is in relation to the difference in the EF of the Ag/PMMA composite and Ag-NP SERS substrates and is due to the existing mismatch between the frequency range of the PMMA opal stop band and the LSPR frequency range of the Ag metal nanoparticles adsorbed on the PMMA opal host matrix. Full article

The DC and AC magnetic susceptibilities of an opal matrix-based nanocomposite with pyrochlore-structured ytterbium titanate particles up to 60 nm in size have been studied in the range of magnetic fields up to 30 kOe. The measurements were performed at temperatures from 2 to 200 K. The temperature dependence of the nanocomposite Yb₂Ti₂O₇ has been found to deviate significantly from the Curie–Weiss law. From the frequency dependence of the AC susceptibility measured in the range from 10 Hz to 10 kHz, the spin relaxation times have been determined, and two relaxation times have been found to be required for the description of the frequency dependence of the susceptibility. The field dependence of the AC susceptibility has been measured. This dependence is proved to be described by the modified Cole–Cole formula. The characteristic fields of the magnetic field dependence of the real part of the susceptibility are determined, the value of the characteristic field being found to increase with increasing temperatures. Full article

The evolution of power generation brings about extensive changes in other parts of the grid, especially in the transmission and distribution components. Within the scope of the Internet of Energy (IoE), electric power flows more flexibly between different parts of the grid. DC power will play an essential role in IoE. Decentralized photovoltaic panels, energy storage, electric vehicle charging stations, and data centers are some of the significant components of future grids dealing with DC power. As a result, power transformers must be appropriately modified to manage power among the different parts of the grid. A power electronic transformer (PET), also known as a solid-state transformer (SST) or smart transformer (ST), is a solution enabling a power grid to deal with this growing complexity. ROMAtrix, as a matrix-converter-based ST, is a developing project targeting future power grids. ROMAtrix realizes the application of a medium voltage (MV) transformer using commercially available power electronic semiconductors. Due to the distinctive features of ROMAtrix and a high number of switches, the implementation of the control system using a single control board is highly demanding. This paper aims to illustrate the implementation, on a field-programmable gate array (FPGA), of pulse width modulation (SVMPWM) applied to the ROMAtrix, considering specific switching patterns. The proposed switching procedure was simulated with PLECS and validated with the hardware-in-the-loop using the OPAL-RT solver. Full article

Opal films with their vivid structural colors represent a field of tremendous interest and obtained materials offer the possibility for many applications, such as optical sensors or anti-counterfeiting materials. A convenient method for the generation of opal structures relies on the tailored design of core-interlayer-shell (CIS) particles. Within the present study, elastomeric opal films were combined with stimuli-responsive photoacids to further influence the optical properties of structurally colored materials. Starting from cross-linked polystyrene (PS) core particles featuring a hydroxy-rich and polar soft shell, opal films were prepared by application of the melt-shear organization technique. The photoacid tris(2,2,2-trifluoroethyl) 8-hydroxypyrene-1,3,6-trisulfonate (TFEHTS) could be conveniently incorporated during freeze-drying the particle dispersion and prior to the melt-shear organization. Furthermore, the polar opal matrix featuring hydroxylic moieties enabled excited-state proton transfer (ESPT), which is proved by spectroscopic evaluation. Finally, the influence of the photoacid on the optical properties of the 3-dimensional colloidal crystals were investigated within different experimental conditions. The angle dependence of the emission spectra unambiguously shows the selective suppression of the photoacid’s fluorescence in its deprotonated state. Full article

In order that the impact on the environment and human beings can be assessed, it may prove necessary for geochemical research work to entail determinations of concentrations of trace elements in building materials, and it is also likely that this will be a time-consuming and financially-demanding business. Additionally, once basic research has been carried out to determine the mineral composition and structural and textural features, it will then be important to determine concentrations of elements that affect the surrounding natural environment and the health of human beings. This paper thus describes mineralogical and geochemical analyses performed on the stone material that opoka rocks represent. Mineralogical studies have shown that the studied opoka rocks most often have cryptocrystalline silica dispersed among carbonate components. The texture of the rock is slightly porous. Silica in the form of type opal A and CT (cristobalite–tridymite) is the main mineral component of the opoka rocks. Carbonate minerals represented by calcite were an important component in the opoka rocks. Earlier geochemical studies focused on the concentration of Sr and Ba. However, the determination of the leachability of these elements as a function of time is a novelty in this study. Trace elements leached from the material matrix were made subject to determinations. The MATLAB program was used to assess leachability in the cases of both strontium and barium, by reference to the Mamdani–Assilian fuzzy algorithm. The presented work has thus sought to experiment with the use of statistical methods to monitor the effectiveness of geochemical processes taking place over time. Full article

Agates in Paleocene/Eocene tuffs from El Picado/Los Indios, Cuba were investigated to characterize the mineral composition of the agates and to provide data for the reconstruction of agate forming processes. The volcanic host rocks are strongly altered and fractured and contain numerous fissures and veins mineralized by quartz and chalcedony. These features indicate secondary alteration and silicification processes during tectonic activities that may have also resulted in the formation of massive agates. Local accumulation of manganese oxides/hydroxides, as well as uranium (uranyl-silicate complexes), in the agates confirm their contemporaneous supply with SiO₂ and the origin of the silica-bearing solutions from the alteration processes. The mineral composition of the agates is characterized by abnormal high bulk contents of opal-CT (>6 wt%) and moganite (>16 wt%) besides alpha-quartz. The presence of these elevated amounts of “immature” silica phases emphasize that agate formation runs through several structural states of SiO₂ with amorphous silica as the first solid phase. A remarkable feature of the agates is a heterogeneous distribution of moganite within the silica matrix revealed by micro-Raman mapping. The intensity ratio of the main symmetric stretching-bending vibrations (A₁ modes) of alpha-quartz at 465 cm⁻¹ and moganite at 502 cm⁻¹, respectively, was used to depict the abundance of moganite in the silica matrix. The zoned distribution of moganite and variations in the microtexture and porosity of the agates indicate a multi-phase deposition of SiO₂ under varying physico-chemical conditions and a discontinuous silica supply. Full article

Agate—a spectacular form of SiO₂ and a famous gemstone—is commonly characterized as banded chalcedony. In detail, chalcedony layers in agates can be intergrown or intercalated with macrocrystalline quartz, quartzine, opal-A, opal-CT, cristobalite and/or moganite. In addition, agates often contain considerable amounts of mineral inclusions and water as both interstitial molecular H₂O and silanol groups. Most agate occurrences worldwide are related to SiO₂-rich (rhyolites, rhyodacites) and SiO₂-poor (andesites, basalts) volcanic rocks, but can also be formed as hydrothermal vein varieties or as silica accumulation during diagenesis in sedimentary rocks. It is assumed that the supply of silica for agate formation is often associated with late- or post-volcanic alteration of the volcanic host rocks. Evidence can be found in association with typical secondary minerals such as clay minerals, zeolites or iron oxides/hydroxides, frequent pseudomorphs (e.g., after carbonates or sulfates) as well as the chemical composition of the agates. For instance, elements of the volcanic rock matrix (Al, Ca, Fe, Na, K) are enriched, but extraordinary high contents of Ge (>90 ppm), B (>40 ppm) and U (>20 ppm) have also been detected. Calculations based on fluid inclusion and oxygen isotope studies point to a range between 20 and 230 °C for agate formation temperatures. The accumulation and condensation of silicic acid result in the formation of silica sols and proposed amorphous silica as precursors for the development of the typical agate micro-structure. The process of crystallisation often starts with spherulitic growth of chalcedony continuing into chalcedony fibers. High concentrations of lattice defects (oxygen and silicon vacancies, silanol groups) detected by cathodoluminescence (CL) and electron paramagnetic resonance (EPR) spectroscopy indicate a rapid crystallisation via an amorphous silica precursor under non-equilibrium conditions. It is assumed that the formation of the typical agate microstructure is governed by processes of self-organization. The resulting differences in crystallite size, porosity, kind of silica phase and incorporated color pigments finally cause the characteristic agate banding and colors. Full article

A typical feature of Wegel Tena opal is the “digit pattern”. This pattern consists of two parts, columns and matrix, with different colours, transparency or play-of-colour effect, which is still unexplained. This study aims at investigating the various parts of the digit pattern using different spectroscopic methods, and scanning and transmission electron microscopy (SEM and TEM). The band at 780 cm⁻¹ on the Fourier transform infrared (FTIR) spectrum is correlated to the symmetric stretching vibration of Si–O. The bands at 1085, 895, 785 and 3600 cm⁻¹ on Raman spectra indicate that Wegel Tena opal is opal-CT. Comparison of the relative intensity of the Raman signals around 360 cm⁻¹ indicates that the microcrystalline opal on the top of the sample contains a higher amount of tridymite-like structural units, and the tridymite-type regions in the matrix contain a higher degree of structural defects. Silica spheres in the columns tend to be smaller and better ordered than in the matrix. The diameter of the silica spheres (d = 80–500 nm) or agglomerates (d = 200–580 nm) in Wegel Tena opal satisfies the conditions of diffraction of visible light, and the thickness of the silica layer (h = 120–200 nm) satisfies the conditions for film interference. Full article

Fieldwork and exploratory study of Poland’s Bełchatów lignite deposit reveals that the Jurassic and Cretaceous sediments with overlying Neogene clays include rocks of greater hardness than the primary composition would indicate. Mineralogical and petrographic tests show the impact of secondary mineralization involving silification in particular. Transitional and carbonate rocks observed microscopically and subjected to X-ray examination show numerous polymorphic forms of silica replacing carbonate minerals. Opal types A and CT, chalcedony, quartz and microcrystalline quartz are all present. The process of silification observed is a selective and multistage one, with selective activity entailing the displacement and replacement of carbonates from older rocks, mainly Cretaceous opoka-rocks and marls, and Jurassic limestones. The opal fills tectonic fractures and has cemented cracked grains. Cathodoluminescence analysis identifies several generations of silica. The rocks have undergone advanced diagenesis as is evidenced by the recorded metasomatic reactions between minerals. They can further be assumed to be in the locomorphic stage. Such observations are relevant to efforts to reconstruct the origin of the rock matrix, and to the study of its textural features. In addition, the tests run on rocks of the lignite series would seem to be of significant value in identifying and developing associated rocks. Full article

Several regions in the High Arctic still lingered poorly explored for a variety of mineralization types because of harsh climate environments and remoteness. Inglefield Land is an ice-free region in northwest Greenland that contains copper-gold mineralization associated with hydrothermal alteration mineral assemblages. In this study, Landsat-8, Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), and WorldView-3 multispectral remote sensing data were used for hydrothermal alteration mapping and mineral prospecting in the Inglefield Land at regional, local, and district scales. Directed principal components analysis (DPCA) technique was applied to map iron oxide/hydroxide, Al/Fe-OH, Mg-Fe-OH minerals, silicification (Si-OH), and SiO2 mineral groups using specialized band ratios of the multispectral datasets. For extracting reference spectra directly from the Landsat-8, ASTER, and WorldView-3 (WV-3) images to generate fraction images of end-member minerals, the automated spectral hourglass (ASH) approach was implemented. Linear spectral unmixing (LSU) algorithm was thereafter used to produce a mineral map of fractional images. Furthermore, adaptive coherence estimator (ACE) algorithm was applied to visible and near-infrared and shortwave infrared (VINR + SWIR) bands of ASTER using laboratory reflectance spectra extracted from the USGS spectral library for verifying the presence of mineral spectral signatures. Results indicate that the boundaries between the Franklinian sedimentary successions and the Etah metamorphic and meta-igneous complex, the orthogneiss in the northeastern part of the Cu-Au mineralization belt adjacent to Dallas Bugt, and the southern part of the Cu-Au mineralization belt nearby Marshall Bugt show high content of iron oxides/hydroxides and Si-OH/SiO2 mineral groups, which warrant high potential for Cu-Au prospecting. A high spatial distribution of hematite/jarosite, chalcedony/opal, and chlorite/epidote/biotite were identified with the documented Cu-Au occurrences in central and southwestern sectors of the Cu-Au mineralization belt. The calculation of confusion matrix and Kappa Coefficient proved appropriate overall accuracy and good rate of agreement for alteration mineral mapping. This investigation accomplished the application of multispectral/multi-sensor satellite imagery as a valuable and economical tool for reconnaissance stages of systematic mineral exploration projects in remote and inaccessible metallogenic provinces around the world, particularly in the High Arctic regions. Full article