Trace Amounts Research Articles

A rapid purification method for trace amounts of cell-free DNA in urine.

Cell-free DNA (cfDNA) is a valuable biomarker for the early detection of genetic diseases and for evaluating treatment efficacy. We developed a rapid and cost-effective purification method for urinary cfDNA using a commercially available DNA purification kit. This method enables the rapid purification (< 20min) of DNA suitable for use in the polymerase chain reaction (PCR) using only a centrifuge and a heater. Additionally, we discovered that short-chain DNA could be efficiently purified by incorporating a concentration step using cationic particles. Quantitative PCR (qPCR) analysis of the purified DNA demonstrated that use of the developed method effectively decreased the DNA detection limit. Overall, this method enables the rapid and inexpensive purification of DNA, and it is suitable for combination with recent advanced DNA analysis technologies such as qPCR, next-generation sequencing, and mass spectrometry. It is therefore expected to contribute to the early detection of cancer and have a major impact on the medical field.

MnO2 nanoparticles enhance the activity of the Zr-MOF matrix electrochemical sensor for efficiently identifying ultra-trace tetracycline residues in food.

Anovel nanobiosensor was constructed by in situ locating nanometer MnO2 particles with controllable size and morphology in a Zr-MOF substrate to serve as an electrochemical probe. The synergistic effect of the two components, Zr-MOFs with high specific surface area and compatibility as a carrier for MnO2, resulted in improved electrochemical activity and excellent electrochemical identification performance for the MnO2@Zr-MOF/GCE biosensor. Under optimized experimental conditions and using CV and DPV technology, the biosensor showed a wide linear detection range (2-200μM), a low detection limit (2.577 × 10-8M), a recovery range (106.26-115.01%), and maximum relative standard deviation (5.155) for tetracycline(TC) identification. The recognition mechanism of the sensor was investigated adopting Laviron adsorption theory. The applicability of the sensor was verified through practical measurements. Overall, the MnO2 @Zr-MOF/GCE sensor possesses the advantages of fast analysis speed, high sensitivity, high selectivity, and simple operation, making it suitable for detecting trace amounts of TC in food.

Evaluation of the Antibacterial and Cell Culture Properties of Anodic Porous Alumina Prepared in Concentrated H2SO4.

The antibacterial activity of anodic porous alumina (APA) prepared using phosphoric, oxalic, and sulfuric acids was tested, and it was found that APA prepared using sulfuric acid had the highest antibacterial activity against Staphylococcus aureus and Escherichia coli. In addition, the results of the antibacterial test using APA prepared with different concentrations of sulfuric acid showed that APA prepared in concentrated sulfuric acid exhibited significantly higher antibacterial activity. APA formed in concentrated sulfuric acid also showed excellent antibacterial activity even at a high culture medium concentration, at which bacterial cells tend to multiply easily. Trace amounts of Al and S that leached out to the culture medium from APA prepared in concentrated sulfuric acid did not affect the antibacterial activity of APA, indicating that the APA surface exhibits excellent antibacterial activity. It was shown that the surface of APA prepared in concentrated sulfuric acid had excellent culture properties for fibroblasts while exhibiting antibacterial activity. APA prepared in concentrated sulfuric acid can be used in various applications that require excellent antibacterial activity as well as on surfaces that suppress bacterial growth and selectively cultivate target cells.

Fine structure of the doublet P levels of boron

We report high-accuracy calculations of the ground and the lowest eight excited Po2 states of the two stable isotopes of the boron atom, B10 and B11, as well as of the boron atom with an infinite nuclear mass ∞B. The nonrelativistic wave function of each of the states is generated in an independent variational calculation by expanding it in terms of a large number, 12000–17000, of all-electron explicitly correlated Gaussian (ECG) functions whose nonlinear parameters are extensively optimized with a procedure that employs analytic energy gradient determined with respect to these parameters. These highly accurate wave functions are used to compute the fine-structure splittings using the first order of the perturbation theory (∼α2), where α is the fine-structure constant, which are then corrected for the electron magnetic moment anomaly (∼α3). As the nonrelativistic Hamiltonian explicitly depends on the mass of the nucleus, the recoil corrections up to the order of α2 are automatically accounted for in the fine-structure calculations. Furthermore, the off-diagonal corrections to the fine structure (∼α4) are estimated using the multireference methods based on one-electron Gaussian orbitals. The results obtained in this paper are considerably more accurate than those available in the literature. Moreover, we report accurate splittings for a number of excited Po2 states, for which there have been no reliable experimental or theoretical data at all. The calculated values presented in this paper may serve as a valuable guide for future experimental measurements of the fine structure of the boron atom. As the fine structure of an atom provides a spectral signature that can facilitate atom's detection, our data can also aid the search for trace amounts of boron in the interstellar medium. Published by the American Physical Society 2024

A Tetrazine Amplification System for Visual Detection of Trace Analytes via Click‐Release Reactions

Achieving visual detection of analytes at ultra‐low concentrations in complex mixtures remains a persistent challenge. While sophisticated techniques offer single‐molecule sensitivity, practical hurdles remain, necessitating tailored signal amplification systems for direct visual detection. In this study, we develop a strategy for the visualized detection of tetrazine through a "click‐release‐oxidation‐cycle" (CROC) cascade amplification process. We systematically describe the construction and synthesis of this system, the kinetic process of click release, the kinetics of oxidation to tetrazine and its cascade amplification effect in trace amounts of tetrazine. This system is capable of amplifying the signal of tetrazine at a concentration as low as 2 nM by 105‐fold, thereby providing a clearly visible purple signal. Finally, as proof of concept, we successfully apply this method to visually detect trace β‐galactosidase (β‐gal) and Pd2+.

A Tetrazine Amplification System for Visual Detection of Trace Analytes via Click-Release Reactions.

Achieving visual detection of analytes at ultra-low concentrations in complex mixtures remains a persistent challenge. While sophisticated techniques offer single-molecule sensitivity, practical hurdles remain, necessitating tailored signal amplification systems for direct visual detection. In this study, we develop a strategy for the visualized detection of tetrazine through a "click-release-oxidation-cycle" (CROC) cascade amplification process. We systematically describe the construction and synthesis of this system, the kinetic process of click release, the kinetics of oxidation to tetrazine and its cascade amplification effect in trace amounts of tetrazine. This system is capable of amplifying the signal of tetrazine at a concentration as low as 2 nM by 105-fold, thereby providing a clearly visible purple signal. Finally, as proof of concept, we successfully apply this method to visually detect trace β-galactosidase (β-gal) and Pd2+.

Ultrasensitive electrochemical detection of thymol using areca nut fibre-derived carbon sensors for environmental protection

The increasing use of thymol (THY) as a common pesticide in agriculture raises significant concerns regarding its potential environmental and human health risks. Therefore, developing a sensitive detection method for thymol residues is essential for monitoring and ensuring safety standards. This study presents a novel approach for sensitively detecting thymol using activated carbon derived from areca nut (Arecanut catechu L) fibre, an agricultural by-product as the precursor. Cetyltrimethylammonium bromide (CTAB) is added to the test solution to improve the material's surface properties and increase the number of active sites. Electrochemical sensing techniques, specifically cyclic voltammetry (CV) and square wave voltammetry (SWV), are employed to evaluate the performance of Cetyltrimethylammonium bromide mediated activated carbon as a thymol detection sensor. The sensor exhibits outstanding sensitivity with an ultralow limit of detection (DL) of 1.84 × 10⁻⁸ M and a limit of quantification (QL) of 6.14 × 10⁻⁸ M, enabling the quantification of trace amounts of thymol in complex matrices. Furthermore, the sensor demonstrates exceptional reproducibility and long-term stability, making it suitable for real-time applications. Utilizing areca nut fibre as a precursor represents a sustainable and eco-friendly approach. This method offers a promising solution for pesticide detection, contributing to enhanced food safety, environmental protection, and regulatory compliance in the agricultural sector.

Mechanism, Kinetics and Modelling of Phenol Carboxylation Reactions with CO2

Combining carboxylation reactions using carbon dioxide (CO2) as a reactant with phenol results in creation of new C-C bonds, and represents one of the most promising routes in sustainable utilization of ubiquitous and readily available resources for production of highly valuable products. This study provides a detailed and well-structured investigation of the effect of various reaction conditions (reactant loading, reaction duration, temperature, CO2 pressure) on the carboxylation of phenol. Sodium phenoxide carboxylation showed well-resolved trends with variation of temperature and time, and resulted in production of salicylic acid (SA) in the range of 11.4 to 47.8%, 4-hydoxybenzoic acid (4HBA) in the range of 2.0 to 8.2%, while the dicarboxylated 4-hydroxyisophthalic acid (4HiPh) was only detected in trace amounts. The effect of the variation of reactant content was shown to be significantly influenced by the reactor size, solid/vessel and gas/solid contact area, as well as the efficiency of the stirring. CO2 pressure was shown to be a crucial element, where reactions carried out below 2 MPa CO2 did not show any activity. While investigating the reaction mechanism, it was shown that the salt analogues of potential products could be acidified in situ by the moisture present, and immediately degraded back to phenol, thus lowering yields of potentially obtained products. The experimental results were successfully used to compose a kinetic model, which very well describes the experimentally obtained results. As such, this study provides a valuable dataset for valorization of lignocellulosic aromatic compounds as well as highly abundant and environmentally detrimental carbon dioxide into industrially valuable mono- and dicarboxylic acids.

Rare‐Metal‐Free Ultrabroadband Near‐Infrared Phosphors

AbstractTrivalent chromium (Cr3+) is an attractive near‐infrared (NIR) emitter, but its ultrabroadband NIR emission is limited to host crystals containing large amounts of rare‐metal elements and usually suffers from low internal quantum efficiency (IQE) and poor thermal stability. Here, a class of high‐performance, rare‐metal‐free ultrabroadband NIR phosphors, are reported by revealing that weak‐field Cr3+ centers featuring broadband NIR emission with near‐unity IQEs are intrinsic, though in trace quantities, to Cr3+ doped MgAl2O4 spinel (MAS) and its derivatives well‐known for their narrowband far‐red emission. It is shown that such weak‐field Cr3+ centers stem from cation inversion ubiquitous in spinel compounds, and their quantity can be increased simply by superstoichiometric Al2O3/Ga2O3. Then SiO2 is introduced into Al2O3‐excess MAS to break the inversion symmetry of Cr3+ centers for greatly improving the probabilities of their otherwise parity‐forbidden 3d–3d transitions. The as‐fabricated phosphor‐converted light‐emitting diodes are capable of emitting ultrabroadband NIR light with high photoelectric efficiency (16.0%) and optical power (180.8 mW), and excellent spectral stability, which apparently outperforms existing state‐of‐the‐art devices.

Facile and in situ production of reduced graphene oxide nanosheets paste electrode via electrochemical exfoliation of carbon paste electrode for fabricating a VEGF165 tumor marker aptasensor

The sensitive detection of trace amounts of vascular endothelial growth factor (VEGF165) in samples holds significant potential for clinical cancer diagnosis across various cancer types. This work introduces a simple, quick, and economical electrochemical method for exfoliating a graphite paste electrode (CPE) to directly synthesize a reduced graphene oxide nanosheet paste electrode (r-GONPE) for the determination of VEGF165. Thionine (Th) was used as a redox probe due to its strong interaction with the graphene surface. The functionalization of r-GONPE by thionine improves its stability while preserving the intrinsic properties of r-GONPE. Au nanoparticles were electrodeposited on the r-GONPE/Th electrode to stabilize the SH-aptamer by self-assembly for selective interaction and to enhance the speed of electron transfer. FESEM images confirmed the formation of a fixed, stable, very thin, and large few-layer reduced graphene oxide nanosheet on the outer surface of the CPE. The surface area of the bare CPE increased significantly after electrochemical exfoliation of the surface graphite layers (from 0.059 cm2 for CPE to 0.281 cm2 for r-GONPE). Electrical characterization showed that the conversion of graphite to graphene resulted in a five-fold increase in peak height and a decrease in peak separation by nearly 30 mV. The selective interaction of the VEGF165 with the r-GONPE/Th/nano-Au electrode modified with SH-aptamer reduced the oxidation peak current of thionine in the DPV signal. Thus, a wide linear calibration ranges from 5.0 pM to 320 pM and a low LOD of 1.03 pM (using the 3σ/S equation) were obtained. The aptasensor demonstrated consistent stability and strong selectivity against typical interferences when detecting picomolar concentrations of VEGF165. It also showed high accuracy and speed in detecting VEGF165 in human serum samples. Additionally, this aptasensor is advantageous due to its cost-effectiveness and simple fabrication process compared to traditional methods that use complex nanocomposites for signal enhancement.

Pharmacological Activities of the Roots of Stemona tuberosa Medicinal Plant: An Overview

: Since childhood, plants and plant products have been used extensively as medicine. The majority of rural residents still rely on natural resources and the old-fashioned medical system for their daily needs. The biological richness of Arunachal Pradesh is renowned, as is its rich cultural diversity. The native population uses a number of aromatic and medicinal plant species to cure a wide range of illnesses. The current review deals with the biological activity of Stemona tuberosa, a possible medicinal plant species of Arunachal Pradesh. Extract from tuberous roots has numerous properties, including anti-bacterial, anti-inflammatory, anti-tobacco mosaic virus, antitussive, wound healing, and anti-herpes. The roots' powder is employed as a preservation and insect deterrent. Alkaloids, sugars and glycosides, phenolic compounds, trace amounts of proteins, saponin, flavonoids, and gum mucilage, were all found during the phytochemical analysis, which shows that the species has a significant potential for therapeutic use. As a result, it is possible to think of the examined species as a potential source of beneficial medications.

Stimulated Pickering emulsion stabilized by binary particles with contrasting wettability and trace surfactant

The investigationof self-assembled particle structures at fluid interfaces has gained considerable interest across various fields. In particular, Pickering emulsions (PEs) stabilized by binary particles co-assembling at these interfaces have attracted even more attention. To explore the self-assembly process of superhydrophobic and superhydrophilic particles at oil–water (O/W) interfaces influenced by a trace amount of surfactant, a series of experiments were conducted. A small quantity (0.01 mmol·L−1) of dodecyltrimethylammonium bromide (DTAB) was introduced, establishing a variable stable emulsion system with high salt tolerance, capable of withstanding up to 6 mol·L−1 NaCl, in synergism with the particles. The DTAB concentration required to stabilize the O/W emulsion with particles was as low as 0.001 mmol·L−1. The stability and type of the resulting emulsion could be adjusted by varying the ratio of hydrophobic to hydrophilic particle (R) or by modifying acid/base conditions. The systems exhibited robust cyclic acid/base regulated demulsification and phase inversion behavior, maintaining stability over at least 10 cycles. Results indicated that the stability and nature of the emulsion were influenced by the curvature of the interface formed by the self-assembled interfacial particle structures, arising from the competitive adsorption of both types of particles and trace surfactant. Further analysis revealed a correlation between interfacial curvature and the surface charges of the particles, which could be modulated through DTAB adsorption. This study elucidated the behavior of hydrophilic and hydrophobic particle self-assembly at interfaces, provided a straightforward strategy for co-preparing switchable emulsions using superhydrophilic and superhydrophobic particles, and expanded the range of amphiphilic particles available for producing PEs. This approach presents significant potential for future research and applications in the field of PEs.

Anti-bacterial efficacy of Boron Nanosheet against clinical isolates and its in vivo toxicity assessment using Artemia salina.

Microbes have been increasing their potential against newly developed drugs and antibiotics daily. The increased microbial drug resistance is still a challenging societal inconvenience. 2D nanomaterials, such as graphene, fascinate researchers with their unique physical and chemical properties and have a major role in current science and technology. Nowadays, researchers have been replacing graphene with its analogous 2D material, borophene, which is a single layer of boron with a honeycomb plane. Boron nanosheets which are theoretically investigated, have been synthesized by various top-down and bottom-up approaches. Our study focuses on synthesizing boron-based material from the precursor MgB2 which possesses a honeycomb boron structure with sandwiched Mg atoms. The Mg atoms have been selectively removed using the chelating agents at alkaline pH. The synthesized boron nanosheets have been characterized by FT-IR, Raman, XRD, FESEM, EDS, and TGA. The formation of B-H-B, B-B and B-O bond is confirmed by FT-IR and Raman spectra. It is also evident from XPS spectra which possess B1s spectra at 193 eV. The efficient chelation and exfoliation is confirmed by EDS and FESEM analysis which shows the presence of Boron and trace amount of Mg with bark like projections. Though there are several studies on antibacterial activity of compounds, generally the studies are with laboratory cultures of bacterial strains. Clinical studies offer more valid results and are very sparse in literature. The use of clinical strains in the present study is one of the novelty. It has also been analyzed for its anti-bacterial activity against clinical strains of B. subtilis, S. aureus, E. coli, and K. pneumonia. Boron nanosheets possess an enhanced zone of inhibition (8mm, 11mm) against clinical strains of B. subtilis where the micro dilution studies show MIC and MBC values as 125μg and 62.5 μg. The in vivo toxicity studies carried out using Brine Shrimp Lethality Assay reveal higher LC50 values of boron nanosheets (>1mg/ml), which in turn portrays its non-toxic nature. Thus, the synthesized boron nanosheets are toxic to multidrug-resistant B.subtilis where it is non-toxic to mammalian cells. Thus, the study could advance the applications of borophene in biomedical applications.

A label-free colorimetric aptasensor for sensitive detection of aflatoxin B1 in peanuts based on dual catalytic hairpin assembly

Aflatoxin B1 (AFB1) is considered one of the most toxic and carcinogenic substances. Developing sensitive and accurate methods for detecting AFB1 in foodstuffs remains a major challenge. Herein, a label-free colorimetric aptasensor was constructed for the detection of AFB1 in peanuts, utilizing dual catalytic hairpin assembly (CHA) for signal amplification. Where, the recognition of AFB1 by its aptamer (Apta) induces the formation of an Apta-AFB1 complex, causing the trigger chain (T) to release from the Apta-T complex. The released T triggers the first CHA reaction in the presence of hairpins H1, H2, and H3, producing H1-H2-H3 complexes. Each sticky end of these complexes serves as the initiating strand for the second CHA cycle, exposing a G-rich sequence from H5 that induces the formation of a G-quadruplex/hemin DNAzyme. This DNAzyme catalyzes the H2O2-mediated oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB), resulting in a color change. Under optimal conditions, the colorimetric signal is linearly related to the logarithm of AFB1 concentration in the range of 50 pM to 1.1 nM, with a detection limit of 13.49 pM. The spiked recoveries for AFB1 in peanuts range from 95.28 % to 104.50 %. This aptasensor provides a sensitive and accurate method for detecting trace amounts of AFB1, which is crucial for ensuring food safety.

Surfactant-Enabled BM particle-embedded coaxial PVDF/PEI electrospun membranes enhancing Lithium-Ion battery safety

In response to the issue of thermal runaway in lithium-ion batteries, a new battery separator with high safety was developed in this study. By incorporating trace amounts of the surfactant sodium dodecyl sulfate (SDS) into the boehmite (BM) slurry, uniform infiltration of the polyvinylidene fluoride/polyetherimide (PVDF/PEI) coaxial electrospun fiber membrane was successfully achieved, thereby significantly enhancing the membrane’s flame retardancy and thermal stability at high temperatures. This method is straightforward and versatile, facilitating a tight integration of BM with individual fibers. Owing to the synergistic effects of the fiber structure, polymer matrix, BM, and binder, the separator also exhibits excellent electrolyte wettability, thermal conductivity, and toughness. Batteries assembled with this membrane demonstrated an initial discharge capacity of 142.1 mAh/g at a 0.5C charge–discharge rate, with a capacity retention of 97.4 % after 120 cycles. This research provides an innovative solution for the fabrication of high-safety lithium-ion battery separators, holding profound scientific significance and promising application prospects.

Electron probe microanalysis of trace sulfur in experimental basaltic glasses and silicate minerals

Abstract Sulfur (S) in the mantle is conventionally assumed to be exclusively stored in accessory sulfide phases, but recent work shows that the major silicate minerals that comprise &amp;gt;99% of the mantle could be capable of hosting trace amounts of S. Assessing the incorporation of trace S in nominally S-free mantle minerals and determining equilibrium S partitioning between these minerals and basaltic melt requires analyzing small experimental phases with low S contents. Here, we develop a protocol for EPMA analysis of the trace levels of S in silicate phases. We use a suite of natural and experimental basaltic glass primary and secondary standards with S contents ranging from 44 ppm to 1.5 wt%. The effects of beam current and counting time are assessed by applying currents ranging from 50 to 200 nA and total counting times between 200 and 300 s at 15 kV accelerating voltage. We find that the combination of 200 nA beam current with a 200 s counting time (80 s peak, 60 s each for upper and lower background, respectively) achieves precise yet cost-effective measurements of S down to a calculated detection limit of ~5 ppm and a blank-derived, effective detection limit of ~17 ppm. Close monitoring of the S peak intensity and position throughout the duration of each spot also shows that high currents and extended dwell times do not compromise the accuracy of measurements, and even low S contents of 44 ppm can be reproduced to within one standard deviation. Using our developed recipe, we analyzed a small suite of experimental clinopyroxenes (Cpx) and garnets (Gt) from assemblages of silicate partial melt + Cpx ± Gt ± sulfide, generated at 1.5 to 3.0 GPa and 1200 to 1300 °C. We find S contents of up to 71 ± 35 ppm in Cpx and 63 ± 28 ppm in Gt and calculate mineral-melt partition coefficients (Dsmin/melt) of up to 0.095 ± 0.064 and 0.110 ± 0.064 for DsCpx/melt and DsGt/melt, respectively. The sulfur capacity and mineral-partitioning for Cpx are in good agreement with SXRF measurements in a prior study by Callegaro et al. (2020), serving as an independent validation of our EPMA analytical protocol.

U-Pb ages of apatite, sulfur isotopes of sulfides and possible origin of the Dashui hematite-rich, sulfide-deficient gold deposit in the West Qinling orogen, Central China

The Dashui gold deposit is one of the largest Au deposits in West Qinling orogenic belt and unique for its hematite-rich and sulfide-rare Au mineralization. The age and genesis of the Dashui Au deposit, however, remain poorly constrained. To resolve these issues, here we present robust apatite U-Pb dating results under the context of detailed textural and compositional studies. The ore mineral assemblages at Dashui consist of fine-grained quartz, hematite, kaolinite, apatite, native Au, and trace amounts of pyrite. The presence of hematite and gold as inclusions fully enclosed in quartz and apatite suggests that the former minerals are of primary origin rather than, as generally considered, a product of supergene oxidation of Au-bearing pyrite. Cathodoluminescence imaging reveals that the ores contain two types of apatite. CL-bright apatite was likely inherited from the magmatic wall rocks, whereas CL-dark apatite precipitated coevally with the ore minerals. In-situ LA-ICP-MS U-Pb isotope analysis of the CL-dark apatite suggests that the Dashui deposit formed at 217.2 ± 4.1 Ma, contemporaneously with the main stage of regional Au mineralization in the West Qinling orogenic belt that formed under the Triassic subduction-collisional tectonic setting. Since the Dashui Au mineralization is temporarily and spatially associated with intermediate to felsic porphyry intrusions, and that the ore sulfides have S isotopes consistent with a magmatic-hydrothermal origin, the deposit can be broadly classified as a Carlin-type Au deposit. Nevertheless, the hematite-rich rather than pyrite-rich ore assemblages indicate an ore-forming environment that was more oxidized than that of typical Carlin-type deposits.

Catalytic effect of the in-situ rhodium(III) complexes in surfactant medium on the auto-oxidation of 1,2-hydroxyphenylthiourea: A theoretical and experimental study for rhodium(III) sensing

1,2-hydroxyphenylthiourea(HPTU) undergoes auto-oxidation to form an yellow colored dimer. The process of auto-oxidation is enhanced by the presence of trace quantities of transition metal ions and transition metal complexes that act as catalysts. In the current study, catalytic potential of rhodium(III) complexes on the auto-oxidation of 1,2-hydroxyphenylthiourea(HPTU) was studied theoretically using quantum mechanical calculations and experiments were carried out using photometry and fluorometry. DFT studies inferred that [Rh(Py)6]Cl3 showed a better catalytic activity in the dimerization of HPTU. Theoretical studies were subsequently validated through experiments using photometric methods and the range of detection was determined to be 6 ng/mL–100 ng/mL. The detection limit was observed to be 2 ng/mL. Analytical parameters such as pH, reagent concentration, metal ion concentration, appropriate activators and surfactants were established.

Study of Seasonal Dynamics of Microcystins and Nutrients in Studena Reservoir in 2023

This paper is a synthesis of data from studies conducted in 2023 on the seasonal dynamics of the presence of microcystin-LR and its homologues in water samples from Studena reservoir. A total of ten samples were collected from June to October 2023. The species composition of phytoplankton and the nutrients total nitrogen and total phosphorus were determined. The presence of microcystins was detected in three samples from the months of September and October (microcystin-LR concentration 0.38 and 0.75 μg/L in the water sample and in a scum at the reservoir wall in October; microcystin-RR 0.10 μg/L in September and 0.55 and 0.70 μg/L in the water sample and in a scum at the reservoir wall in October; microcystin-YR 0.27 and 0.48 μg/L in the water sample and in a scum at the reservoir wall in October). Trace amounts of microcystin-LR equivalents other than microcystin-RR and microcystin-YR were observed in water samples in June and July. The phytoplankton communities in the reservoir are persistently inhabited by blue-green algae. The presence of microcystins at concentrations close to the permissible level in the autumn sample indicates that at the time of sampling the bloom of cyanobacteria that produced the microcystins had passed and the toxins released remained in the water. Due to the near acceptable concentration of MC-LR in the autumn sample, serious consideration should be given to monitoring the reservoir during periods favourable for bloom formation.

Optimizing the mechanical properties of Al4SiC4 ceramics: A study on incorporating Y2O3 and spark plasma sintering

The present study focuses on optimizing the mechanical properties of Al4SiC4 ceramics by incorporating Y2O3 additives and utilizing spark plasma sintering. A native oxide layer, predominantly composed of Al2O3 with trace amounts of SiO2, was detected on the surface of the Al4SiC4 powder. Following sintering at 1823 K, Al4SiC4 was identified as the dominant phase, with Y3Al5O12 (YAG) recognized as the secondary phase. The effects of YAG on grain growth in Al4SiC4 is clarified based on experimental findings and molecular dynamics simulations. Additionally, the presence of SiO2 within the native oxide layer of Al4SiC4 is examined from both microstructural and thermodynamic perspectives. Precise optimization of the Y2O3 content is essential for enhancing mechanical properties, with an optimal content of 3 wt% yielding maximum values of flexural strength and fracture toughness at 436 MPa and 4.0 MPa·m1/2, respectively, along with Vickers hardness values of 12.0 GPa.