Difference In Melting Temperature Research Articles

Utilizing foxtail millet husk waste for sustainable new bioplastic composites with enhanced thermal stability and biodegradability

Foxtail millet husk (FMH) is a byproduct that is not suitable for consumption and is often discarded as solid waste. However, it can be used as a raw material to develop novel bioplastic composites that transform agro-based leftovers into value-added goods. Herein, new bioplastic composites were developed from poly(lactic acid), poly(butylene adipate-co-terephthalate) and FMH based granules by Injection Molding. The required granules were generated via a solvent evaporation method. The resulted bioplastic composites were analyzed for their morphologies, mechanical properties, crystal structures, thermal stability, and melting and crystallization behaviors using various techniques, such as scanning electron microscopy, universal testing machine, X-ray diffraction, thermogravimetric analysis, and differential scanning calorimetry. Expressly, chemical bonding between FMH fibers and poly(lactic acid)/poly(butylene adipate-co-terephthalate) PLA/PBAT was confirmed through Fourier Transform infrared spectroscopy analysis. The inclusion of FMH lowered the impact strength of the PLA/PBAT combination, which was confirmed by mechanical analysis. Morphological findings confirmed that the PLA/PBAT combination had FMH aggregation. DSC thermograph revealed negligible differences in glass transition and melting temperatures of PLA/PBAT blend with and without FMH. The thermogravimetry results exhibit that the FMH can improve bioplastic thermal stability. The addition of FMH improved the biodegradability of the PLA/PBAT bioplastic composites. Overall, FMH waste can be repurposed for bioplastic composites with enhanced thermal stability and biodegradability. This reduces solid waste from agricultural practices and creates eco-friendly products. Further research could lead to more sustainable alternatives.

Enhancement of processed cheese quality using ultrasound: energy density optimization and industrial applications

This study examined the impact of varying ultrasound energy densities on the functional properties of processed cheese with different levels of emulsifying salt (0%, 0.5%, 1%, 2%, or 3% disodium phosphate). The mixtures were ultrasonicated at 65 watts and 160 watts for either 3 min or 9 min, producing energy densities of 58.5 J/g, 175.5 J/g, 144 J/g, and 432 J/g. The rheological and textural properties of the processed cheese were evaluated at these energy densities and compared to a control sample. At 432 J/g, cheese with 1% emulsifying salt was cooked whereas cheese at 58.5 J/g, 175.5 J/g, and 144 J/g did not cook with the emulsifying salt levels of 1% or lower. There was no significant difference (p > 0.05) in hardness and melting temperature between cheese having the energy density of 432 J/g and processed with 1% and 2% emulsifying salt. Additionally, no significant difference (p > 0.05) was observed in the functional properties of cheese across different energy density treatments. The functional properties of the processed cheese improved significantly with increased emulsifying salt levels. This study suggests that using 432 J/g of ultrasound energy can effectively reduce the requirement of emulsifying salts in the cheese industry.

Отримання жароміцного гомогенного сплаву методом пресування та спікання суміші порошків (Nb-21Ti-5Al-10Cr-7Mo) ат. %

Multicomponent high temperature strength alloys of the Nb-Ti-Al system, alloyed with Cr, Zr, Mo and Si, with a specific gravity of 6.3 - 7.4 g/cm3, have proven extremely promising in aviation and space technology. However, their physical and chemical features are associated with the high activity of the components, with a significant difference in melting temperatures (from Tmel. Mo – 2617 °C to Tmel. Al – 660 °C) and different specific gravity (from 10.2 g/cm3- Mo up to 2.7 g/cm3- Al), is a big problem for their production. The long crystallization interval of cast alloys of this system, thermophysical features of their crystallization, determine the possibility of formation of dendritic structures, the development of dendritic liquation and segregation of low- or high-temperature intermetallics and eutectics, the tendency to the formation of crystallization cracks, which reduces the operational characteristics of cast alloys. In this regard, it became necessary to investigate the possibilities of obtaining an alloy by the method of powder metallurgy. The purpose of this work was to obtain a homogeneous alloy, to study changes in the grain structure, phase transformations and mechanical properties of the material at various stages of processing in the process of obtaining a homogeneous alloy structure by powder metallurgy methods. The need to protect powder components from oxidation, formation of nitrides, carbides during technological operations at temperatures above 200 °C (high-purity argon) has been established. The optimal duration of intensive grinding of a mixture of powders and granules of raw materials has been worked out, which makes it possible to control the uniformity of the size of the particles of the mixture components, porosity and homogeneity of the alloy. The optimal duration of grinding is 30 minutes, during which the most homogeneous mixture in terms of particle size is formed. The optimal annealing mode was established, which ensures the achievement of homogenization of the alloy, phase transformations at the boundaries of the contact of component particles, and changes in grain sizes. Microstructural and X-ray structural analysis of the samples was carried out, their microhardness and grain dispersion were determined. Keyword: high-temperature strength niobium alloys, physical and chemical features, powder metallurgy, homogeneity, microstructure, mechanical properties, phase composition.

Friction stir spot welding of recycled scrap thermoplastics

There is a real demand for sustainable lightweight structures because of the growing environmental concerns. One important solution is developing structures through recycled scrap/waste thermoplastic materials. The current work studies the friction stir spot weldability of recycled thermoplastics, which will help to analyze the potential of friction stir-based welding techniques towards developing these sustainable structures. The combined behavior of recycling-welding procedures is investigated, as they may cause degradations; to ensure that the base thermoplastic polymer's chemical, thermal, and mechanical properties are retained. Scrapped milk bottles made from HDPE material are used as a case study. The highest lap-shear load of 1528 N was achieved at the optimum welding conditions of 1600 rpm rotational speed, 1 mm plunge depth, and 60 s dwell time. Fractographic studies (macroscopic and SEM-based) suggested four types of fracture morphologies depending on welding conditions used. The DSC results showed no significant differences in melting temperature and crystalline content of the polymeric material. The TGA tests showed no significant thermal degradations. The FTIR analysis of all the samples (bottle, recycled sheet, weld material) exhibited characteristic HDPE peaks. All these results suggest combined-welding recycling had a minimal impact on the polymeric structure. Thus, friction stir spot welding (FSSW) technique joins recycled thermoplastic scrap/waste materials with high lap-shear load and without any significant polymer degradations.

Molecular dynamics simulation study on non-equilibrium melting of sodium crystals at high heating rates

ABSTRACT The non-equilibrium melting of Na crystals at high heating rates and the evolutions of the atomic clusters are studied by the MD method and PTM analysis. Results show that as the heating rate rises from 1 × 1011 K/s to 2 × 1013 K/s, the non-equilibrium melting temperature of Na increases non-linearly from 417 K to 480 K, the melting temperature difference experienced increases from 7 K to 27 K, while the melting time decreases from 70 ps to 1 ps. Through the PTM analysis, it is found that some BCC clusters transform into the disordered Other clusters through intermediate HCP and FCC clusters with increasing temperature, and the BCC cluster's reduction rate and the Other cluster's growth rate are getting slower with increasing heating rate. There is a good correspondence between the evolutions of the atomic clusters, the changes of macroscopic physical parameters, and the peaks and valleys of RDF with temperature.

Mechanically induced self-propagating reactions (MSRs) to instantly prepare binary metal chalcogenides: assessing the influence of particle size, bulk modulus, reagents melting temperature difference and thermodynamic constants on the ignition time

Mechanically induced self-propagating reactions (MSRs) of metal chalcogenides can be completed within few minutes and seem to be partly governed by particle size distribution and bulk modulus of the reagents.

Effect of Defocusing Distance on Microstructural, Hardness, and Tribological Behavior of Ni-Cr-Si-B-C Powder Deposit on 316LN Austenitic Stainless Steel Substrate Using Laser Hard-Facing

The Ni-based alloy powder has been melted and bonded to an AISI 316LN austenitic stainless steel (ASS) base material (substrate) using a high-energy disc laser with a maximum power of up to 12 kW. The substrate’s hard-faced reservoir is highly diluted due to the significant difference in melting temperature between the substrate and the commonly used Ni-based alloy. The hardness, macrostructure, microstructure, and wear resistance effects of the defocusing distance were examined. The composition, microstructure, hardness, and wear resistance of phases have been examined with a pin-on-disk wear test, an energy dispersion spectroscopy (EDS), a scanning electron microscope (SEM), and X-ray diffraction (XRD). According to the findings, the height and diameter of the beads rose when the distance was increased from 17 mm to 37 mm. On the other hand, penetration and dilution decreased from 3.7 mm to 2.7 mm and from 9.7% to 3.1%, respectively. When the defocusing length is increased and the penetration profundity and dilution are limited, the density of energy per unit clad is accessible. The laser hard-faced surfaces contain microstructures of Ni-rich solid solution, boride, and carbide. These different factors cause higher hardness and resistance to wear.

Utilization of Torrefied and Non-Torrefied Short Rotation Willow in Wood-Plastic Composites.

The torrefaction process is widely used in the energy field, but the characteristics of the torrefied wood also have positive effects on the production of wood plastic composites. In this study, short-rotation shrub willow was torrefied at 225 and 300 °C and incorporated into polypropylene composites filled with changing levels of weight percent (wt%) of non-torrefied and torrefied (5, 15, 25, and 40 wt%) wood. Nine different formulations were extruded for mechanical, thermal, and water absorption properties. The tensile properties of composites were not affected by any level of torrefaction, while higher flexure properties were in favor of lower wt% of torrefied wood. The slowest rate of thermal degradation was confirmed for the highest wt% of torrefied wood with a torrefaction temperature of 300 °C. In contrast, the presence of torrefied wood in composites did not show a difference in crystallization or melting temperatures. The most noticeable contribution of torrefaction temperature and wt% was found for water-absorbing properties, where the higher torrefaction temperature and largest wt% of torrefied wood in the composite resulted in decreased water uptake.

A peptide nucleic acid probe-based multiplex qPCR assay for rapid and accurate detection and quantification of fish-pathogenic Edwardsiella species

Edwardsiellosis causes severe economic losses in the aquaculture industry worldwide. Accurate identification of the fish pathogenic Edwardsiella species is crucial for preventing disease spread and providing effective treatment strategies in the aquaculture industry. These species have high phenotypic and genetic similarities (> 99% in 16S rRNA sequences), which makes their differentiation challenging. In this study, we developed a multiplex real-time PCR diagnostic assay based on the single-copy DNA gyrase subunit B (gyrB) gene using a peptide nucleic acid (PNA) probe to discriminate among four fish pathogenic Edwardsiella species, E. tarda, E. piscicida, E. anguillarum, and E. ictaluri. Through phylogenetic analysis based on gyrB sequences (1462 bp), 57 Korean Edwardsiella isolates were affiliated to E. piscicida, E. anguillarum, and E. tarda, accounting for host and geographical origin specificity. The assay targeted a conserved region in gyrB, and designed four probes, each capable of distinguishing among the four Edwardsiella species, even in cases of 1–3 nucleotide mismatch, based on differences in melting temperature. The assay exhibited high specificity and sensitivity, with reaction efficiency in the range 85–100% and a reliable quantifiable limit of 102 copies per reaction for all fluorescence signals. In addition, it could detect and quantify the four species, even in mixed infections, allowing accurate identification within 2 h in a single reaction. This PNA probe-based multiplex qPCR assay could be a practical and reliable diagnostic tool in the field and provide correct taxonomic assignment for further research on the widened host range and niche, pathogenicity, and susceptibility of each Edwardsiella species, to help establish appropriate treatment and vaccine strategies.

Interdiffusion between 316L Stainless Steel and Copper in Coatings Processed by High Velocity Oxyfuel

Abstract Joining of stainless steel and copper is of interest to a variety of applications that range from heat exchanger to nuclear waste container. Nevertheless, welding of these dissimilar metals is challenging because of the risk of hot cracks and lack of fusion associated with their differences in melting temperatures and thermal conductivities. In this work, joining of 316L stainless steel and copper by high velocity oxyfuel is investigated using two systems of materials, the first consisting of copper coatings on AISI 316 substrates, and the second of 316L coatings on copper substrates. To promote metallurgical bonding, the systems were exposed to 500°C, 700°C, 900°C, and 950°C for 10 h under flowing argon atmosphere. Microstructure was characterized by optical and scanning electron microscopy and energy-dispersive x-ray spectroscopy. Bending tests were carried out to qualitatively investigate the coatings adhesion and cohesion strength. It was found that 316L coatings have a much superior adhesion to copper substrates than copper coatings had to AISI 316 substrates, associated with the ease of 316L incoming particles to embed in the softer copper matrix and with the higher susceptibility of 316L coatings to diffuse into copper substrates. In contrast, in copper coatings, copper oxides formed during deposition decomposed during heat treatment, releasing oxygen that caused porosity and oxidation on the interface with the stainless-steel substrate, preventing the formation of a clean metallurgical bond. Diffusion of iron-rich oxide inward the copper coating was also observed near the interface, indicating that diffusion of steel into copper is more likely than diffusion of copper into steel. Nevertheless, heat exposure was found to increase damage tolerance of copper coatings, associated with a higher coating ductility and compliance.

Orientation-dependent phase transition pathways of single-crystal nickel over large shock range

The response of single crystals to increasing shock strength involves complex phase transition processes from solid-solid to solid-liquid phases. However, it is not yet fully understood how these phase transitions occur along different crystallographic orientations, and what the dominant micro-mechanisms are at different shock stages. To fill this knowledge gap, non-equilibrium molecular dynamics simulations are performed to explore the dynamic phase-transition characteristics of face-centered cubic Ni single crystal over a large shock strength range of 0–350 GPa. The orientation-dependent phase transition in single-crystal Ni is examined through three typical shock directions: [001], [011], and [111], and a phase-transition locus map is established. The results show that the shock compression of single-crystal Ni undergoes four response stages: (I) elasticity, (II) plasticity, (III) partial melting, and (IV) complete melting. The shock orientation plays a crucial role in the shock wave structure, Hugoniot, microstructure evolution, and shock melting behavior. The [001] shock direction maintains a single-wave structure and exhibits a shear stress superelasticity. However, the [011]/[111] orientations undergo a single-double-single wave transformation, and an interesting U-shape transition wave is identified along the [111] orientation due to its unique progressive plasticity. Superheating and cold melting phenomena are observed along the [001] and [011]/[111] orientations, respectively. The differences in the critical melting temperature and threshold shock pressure along different orientations are up to ∼3000 K and ∼80 GP. Atomic-structure analysis reveals that due to the Bain path, FCC→BCC (BCT) is the dominant solid-solid phase transition along the [001] orientation, and the dislocation slips are limited in a narrow shock window. Melting nuclei emerge, grow, and coalesce homogeneously on the BCC (BCT) substrate, leading to the superheating phenomenon. In contrast, a dynamic process involving shock melting and recrystallization is observed along the [011]/[111] orientations, which finally results in the coexisting of the solid and liquid phases. Heterogeneous melting, marked by mixed phases, is the most distinctive feature in the [011]/[111] orientations, which is responsible for the cold melting phenomenon. Our study shed light on the shock-induced phase transitions of FCC single crystal, which may offer insight into understanding the complex polycrystalline.

Evaluation of Tungsten—Steel Solid-State Bonding: Options and the Role of CALPHAD to Screen Diffusion Bonding Interlayers

Critical aspects of innovative design in engineering disciplines like infrastructure, transportation, and medical applications require the joining of dissimilar materials. This study investigates the literature on solid-state bonding techniques, with a particular focus on diffusion bonding, as an effective method for establishing engineering bonds. Welding and brazing, while widely used, may pose challenges when joining materials with large differences in melting temperature and can lead to mechanical property degradation. In contrast, diffusion bonding offers a lower temperature process that relies on solid-state interactions to develop bond strength. The joining of tungsten and steel, especially for fusion reactors, presents a unique challenge due to the significant disparity in melting temperatures and the propensity to form brittle intermetallics. Here, diffusion characteristics of tungsten–steel interfaces are examined and the influence of bonding parameters on mechanical properties are investigated. Additionally, CALPHAD modeling is employed to explore joining parameters, thermal stability, and diffusion kinetics. The insights from this research can be extended to join numerous dissimilar materials for specific applications such as aerospace, automobile industry, power plants, etc., enabling advanced and robust design with high efficiency.

Experimental and numerical investigation of PCMS on ceilings for thermal management

In this study, experimental investigation of phase change materials (PCM) integrated into building on ceilings was assessed for thermal management capabilities by comparing two building test models with and without PCM based on fluctuation in PCM temperatures owing to ambient temperature variations. Commercial organic PCM (OM-30) with a peak melting point of 31.10 C was used as PCM with high-density polyethylene (HDPE) as the encapsulation. Differential scanning calorimeter (DSC) was used to examine the thermophysical characteristics of PCM such as phase transition temperature, latent heat, and specific heat capacity. The various PCM temperature ranges included for the study are (i) Above phase change melting temperature range ii) within Phase Change melting temperature range iii) Proximity to PCM onset melting temperature range iv) proximity to PCM end melting temperature range. Under free-floating ambient Condition, the indoor air temperature was dropped in PCM installed room up to 1.69 °C, 5.79 °C, 2.26 °C, & − 2.87 °C compared to without PCM room for a PCM Melting temperature difference of 8.77 °C,1.55 °C, 1 °C & 0.44 °C respectively. Also, it was divulged that the PCM utilized 3.2%, 31.4%, 6.9%, & 12.27% of the total latent heat energy deployed in order to produce a temperature difference of 1.69 °C, 5.79 °C, 2.26 °C, & − 2.87 °C compared to without PCM room.

Laser welding of dissimilar materials - simulation driven optimization of process parameters

Laser welding can be used to join dissimilar materials to produce lightweight structures, and electric vehicle battery systems, which are important means of limiting the carbon emissions in the transport industry. Due to the differences in melting temperatures, thermal conductivities, and mutual solubility of dissimilar materials, it is still challenging to create defect-free joints with high mechanical strength, or low contact electrical resistance. In this work, we present a state-of-the-art numerical model of laser welding, developed within the Computational Fluids Dynamics (CFD) paradigm. The multi-physics model simulates melting, flow, and solidification of the alloys and accounts for the laser-material interactions, phase change, temperature and alloy-dependent thermophysical properties, recoil pressure, buoyancy force, and Marangoni effect. The simulation predicts weld penetration depth and width, alloy mixing, as well as the temperature gradient and cooling rate during the solidification that can be further fed into a micro-structure prediction model. The model is coupled with an optimization tool, which iterates over different process parameters to optimize the joint. The methodology is presented for steel to aluminium welding in lap configuration, but it can be used for other materials such as steel-copper, aluminium-copper, or steel-nickel, and in arbitrary geometrical configuration.

Effect of enhancement in metal foam pore density on heat transfer of phase-change materials

To explore the effect of metal foam(MF)pore density on the melting and heat transfer of phase-change materials(PCMs), a semi-cylindrical visualization experimental setup was established to experimentally study copper MFs with different pore densities coupled with paraffin wax. The results showed that as pore density increases, the melting time of the composite PCMs decreases compared to that of pure paraffin wax by 11.5%, 16.2% and 18.1% for pore densities of 5, 20, and 30 PPI, respectively. Composite PCMs with a pore density of 30 PPI exhibited fastest melting and lowest maximum temperature difference during melting. Considering the relative thermal energy storage(TES) capacity and relative TES rate, composite PCMs with a pore density of 30 PPI exhibited optimal overall thermal storage performance. Furthermore, heat conduction was the primary means of thermal transmission during the melting of the bottom paraffin. However, the melting of the upper paraffin was nevertheless influenced by natural convection, Hence, as pore size decreased, the influence on the weakening of natural convection became more significant. The results of the study provide guidance for the optimal design of latent heat storage devices for semi-cylinders.

Structural & thermal study of Sb14Se(86-x)Sn(x) chalcogenide glassy system

The structural and thermal analyses of Sb14Se(86-x)Sn(x) (x = 3 and × = 6) glassy system generated by the usual melt-quenching approach are presented in this study. Using the differential scanning calorimeter (DSC) technology, the crystallisation mechanism of the produced glass samples were investigated. With increasing Sn content there is increase in glass transition temperature Tg. The less difference in melting temperature and crystallisation temperature makes prepared glasses suitable for memory switching devices. At room temperature the infrared transmission spectra of Sb14Se(86-x)Sn(x) (x = 0, 3, 6, 9, 12 and 15) chalchogenide glasses were acquired in the 2000–2500 cm−1 spectral range. With Sn addition, far IR spectra are shifted towards the high frequency side and some new bonds appear. Because it was evident that Se atoms were being replaced by Sn atoms, a corresponding rise in the production of Sn-Sn bonds and a subsequent fall in Se-Se bonds were seen. The glasses produced in this manner exhibit improved glass forming capability and strong thermal stability. There was good agreement between experimental data and theoretical estimations of bond energy, relative likelihood of bond formation, and wave number. [copyright information to be updated in production process]

ANALYSIS OF NEW PRIMER PAIR CANDIDATES OF rbcL GENE FOR IDENTIFICATION OF MICROALGAE SCENEDESMACEAE

Scenedesmaceae is one of the microalgae groups that has been widely studied as promising biodiesel feedstock. Its morphological identification is often confused by environmental changes, so it requires molecular identification as well. The current study aimed to obtain primer pair candidates that identify the Scenedesmaceae based on the rbcL gene. The research used bioinformatics tools, which harvested rbcL protein sequence data, performed multiple sequence alignments, and designed primers based on conserved and less-conserved regions. The best left and right primers selected based on sequence length, melting temperature, 3' end stability, number of hairpins, and self-dimers, were paired, and three candidates were obtained. The three pairs were examined based on melting temperature difference, number of hetero-dimers, length of amplified nucleotide product, number of hits, and number of genera captured from the GenBank. Sce-16 (F, 5'-TGGTCGTGCTGTTTATGAATGT-3' and 1_RL, 5'-TGCCAAACATGAATACCACCA-3'), which is back-translated according to Hariotina sp. (AOY36008.1), is the most preferred candidate compared to the other two pairs after discussing their advantages and disadvantages. In the future, the proposed primer candidate needs to be validated through in vitro amplification with some optimizations to eliminate potential weaknesses.

Effects of different sources of cellulose on mechanical and barrier properties of thermoplastic sweet potato starch films

Sweet potato starch and different celluloses were mixed by thermoplastic extrusion and then thermoplastic starch/cellulose composite films were prepared using a casting method. The effect of different celluloses on the mechanical and barrier properties of thermoplastic sweet potato starch films were studied and compared. The results indicated that among thermoplastic starch/cellulose composite films, the hydrogen bond interaction between starch and sugarcane cellulose was more obvious and the crystallization melting temperature difference was smaller, indicating better compatibility between sugarcane cellulose and sweet potato starch. Thermoplastic starch/sugarcane cellulose film had the largest FTIR ratio values of 1047 cm−1/1022 cm−1, resulting in the highest tensile strength (3.75 MPa), largest contact angle (68.44°), or stronger surface hydrophobicity. Thermoplastic starch/cornstalk cellulose film had the highest thermal degradation temperature (325 °C). Thermoplastic starch/wheat or bamboo cellulose film had lower UV transmittance (about 36%), indicating stronger UV Resistance. Thermoplastic starch/rice bran cellulose film had the largest elongation at break value (49.03%). Thermoplastic starch/bamboo or cornstalk cellulose films had lower water vapor permeability, whereas thermoplastic starch/rice bran cellulose had higher water vapor permeability. The outcoming would provide a new theoretical basis for choosing an optimal cellulose compatible with thermoplastic sweet potato starch to enhance mechanical properties, water resistance and barrier property of thermoplastic starch films.

Collective dynamics in the lipid phases of DMPC/cholesterol bilayers: A neutron spin-echo study.

Cholesterol is essential in cell membranes as it regulates membrane structural and material properties such as phase behavior, elasticity, and viscosity. Cholesterol levels in different organelles vary, from less than 5% in mitochondria to 40% in the plasma membrane of eukaryotic cells. According to an experimental phase diagram of 1,2-dimyristoyl-sn-glycerol-3-phosphocholine (DMPC)/cholesterol mixture based on lateral diffusion measurements from early studies, at the above melting temperature, the system undergoes a phase transition from a liquid-disordered (Ld) phase to a liquid-ordered (Lo) phase with a coexisting phase (Ld+Lo) in between upon increasing cholesterol concentration [1]. Our work attempts to understand the collective dynamics of the mixture in each phase and quantify their behavioral trends. We first performed densitometry to determine the mixture's molecular volume and to correct the melting temperature difference between protiated and deuterated DMPC, which was used in neutron experiments. The molecular volume was then implemented in small angle neutron scattering (SANS) experiments and data analysis to extract the area per lipid (AL) and thickness of the lipid mixture in each phase region. Finally, neutron spin echo (NSE) is used to access the dynamic properties by adopting structural information from SANS. The NSE results show the effective bending modulus and membrane viscosity of the Ld phase scale with AL, as observed in our previous study of mixed lipid membranes [2].

A modified high-resolution melting-based assay (HRM) to identify the SARS-CoV-2 N501Y variant

High-resolution melting (HRM) analysis is a PCR–based method that can be used as a screening assay to identify SARS-CoV-2 variants. However, conventional HRM assays hardly detect slight melting temperature differences at the A–T to T–A transversion. As the N501Y substitution results from A–T to T–A transversion in A23063, few or no studies have shown that a conventional HRM assay can identify N501Y variants. This study successfully developed an HRM assay for identifying the N501Y mutation. Two HRM assays were used in the N501 site because the discrimination results were affected by the virus copy numbers. One is a conventional HRM assay (detectable at 103–106 copies/mL) and the other is a modified HRM assay by adding the wild-type fragment (detectable at 105–1010 copies/mL). Using viral RNAs from cultured variants (Alpha, Beta, and Gamma), a modified HRM assay correctly identified three N501Y variants because of high-copy-number RNAs in those viral samples. The sensitivity and specificity of the N501Y assay were 93.3% and 100%, respectively, based on 209 clinical samples (105 for N501; 104 for N501Y). These results suggest that our HRM-based assay is a powerful tool for rapidly identifying various SARS-CoV-2 variants.