High Resistance Research Articles

Development of double-layer rotors for asynchronous drives of mining and transport machines

Due to the simplicity of the design and high energy indicators, asynchronous electric motors (AM) are the main consumers in the power supply systems of mining enterprises. Large starting currents of motors lead to heating and damage to the insulation of the stator windings. An urgent problem to improve the reliability of mining and transport machines is the development of AM, providing smooth transients with increased starting torque and reduced starting current. In an AM with a closed-loop rotor, a magnetic conductor is performed by a charged cylinder on the rotor shaft, which is made of electrotechnical steel with high magnetic permeability. The electrical conductor is often a squirrel cage-type short-circuited rotor made of a material with high specific conductivity. A technology has been developed for producing ferro-copper alloys for the active outer cylinder of a double-layer rotor, replacing a "squirrel cage". These alloys combine the properties of an electric current conductor and a magnetic flux. This allows us to obtain the effect of displacement and reduction of current in the rotor, which is accompanied by an increase in the effective resistance of the rotor and the electromagnetic torque during the start-up process. Full-scale experiments have been carried out with asynchronous motors with various rotors having a displacement effect. Motors having double-cage or deep-groove rotors develop an increased starting torque at a relatively lower starting current. The starting quality of these motors is, on average, 1,5 times higher than that of a motor without current displacement. Replacing a double-cage rotor with a double-layer rotor leads to a decrease in the starting current by 25% and an increase in the starting torque by an average of 2,5 times. The quality factor of starting an asynchronous motor with a double-layer rotor is 3-4 times higher than the quality factor of starting similar motors with a conventional rotor cage without current displacement, 2-2,5 times compared with a double cage or a deep groove and 1,3-1,5 times compared with a rotor with a high electrical resistivity. The use of double-layer rotors limits voltage fluctuations in the network, ensures a reliable, smooth start, eliminates vibration and extends the service life of all equipment.

Electrochemical Machining of Micro-Pit Arrays on a GH4169 Alloy with a Roll-Print Mask Using a C6H5Na3O7-Containing NaNO3 Mixed Electrolyte

GH4169 alloy, a nickel-based superalloy known for its excellent high temperature resistance, corrosion resistance, mechanical properties, and high-temperature tribological properties, is widely used in industrial applications, such as in gas turbines for space shuttles and rocket engines. This study addresses the issue of electrolyte product residue in the electrochemical machining process of a GH4169 alloy by utilizing a C6H5Na3O7-containing NaNO3 new mixed electrolyte. Comparative investigations of the electrochemical behavior and electrolyte product removal mechanisms at different concentrations of C6H5Na3O7 additive in NaNO3 solutions were conducted. The effects of additives, applied voltage, and the rotating speed of the cathode tool on the processing performance of micro-pit arrays on a GH4169 alloy were analyzed. The results indicate that the mixed solution containing C6H5Na3O7 significantly improves the localization and geometric morphology of the micro-pits compared to a single NaNO3 solution. The optimal electrochemical machining parameters were identified as 0.5 wt% C6H5Na3O7 + 10 wt% NaNO3 mixed electrolyte, 12 V applied voltage, and 0.1 r/min rotating speed of the cathode tool. Under these conditions, high-quality micro-pit arrays with an average diameter of 405.85 μm, an average depth of 87.5 μm, and an etch factor (EF) of 1.67 were successfully fabricated, exhibiting excellent morphology, localization, and consistency.

MONOCRYSTALLINE DIAMOND MEMBRANES WITH A THICKNESS OF 10 MICRONS, MANUFACTURED BY PLASMA ETCHING

New applications of high-quality synthetic diamond in sensors and integrated photonic circuits, which are being rapidly developed nowdays, often demand freestanding diamond membranes with a thickness of about 10 microns as a substrate. However, the process of thin single-crystal diamond membranes fabrication, as well as their subsequent processing are challenging due to the high hardness, chemical resistance and brittleness of the material. Our work demonstrates a method for creating freestanding diamond membranes mounted on a thick diamond substrate using reactive ion etching of single-crystalline diamond wafers in plasma with mechanical protective masks. The optimal thickness of a diamond wafer for membranes etching is determined in the range from 100 to 120 µm with mandatory plane-parallel polishing of the sides. We experimentally studied the interaction of RF discharge SF6 based plasma with diamond surface during deep etching with mechanical protective masks of various shapes. It was found that the use of thick masks leads to an uneven rate of diamond etching over the entire area of the formed membrane. We have assessed ion sputtering resistance of various mask materials in SF6 based plasma, and found the most promising mask materials for deep diamond etching (steel, copper, diamond). We have fabricated diamond membranes with a thickness of 11,5 µm (and more), mounted on a durable 60 µm (and more) thick frames, and studied their characteristics. After etching membrane surface roughness was less than 25 nm, and the unevenness of their thickness did not exceed 20%. Also, we compare different methods for controlling the depth of diamond etching and the thickness of the resulting membranes, including mechanical measurements, IR spectral reflectometry, optical profilometry and electron microscopy. For citation: Golovanov A.V., Yun M.I., Bondarenko M.G., Prosin A.A., Tarelkin S.A. Monocrystalline diamond membranes with a thickness of 10 microns, manufactured by plasma etching. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 10. P. 55-64. DOI: 10.6060/ivkkt.20246710.1y.

Development and evaluation of a new winter bread wheat variety Rubin Dona according to the main economically valuable traits

Relevance. The development of new varieties and their rapid introduction into production remains the most effective resource for improving productivity, energy saving, profitability and competitiveness. The purpose of the current study was to develop the winter bread wheat variety Rubin Dona and evaluate its productivity and basic adaptive, technological, and baking properties.Methods. The current study was carried out in the fields of research crop rotation of the department of winter wheat breeding and seed production in 2018–2023. The variety was developed by the method of intravarietal hybridization using the productive and adaptive variety Nakhodka as a maternal form and the high-quality strong wheat variety Donskaya Yubileynaya as a paternal form and a subsequent individual selection.Results. There has been established that the variety Rubin Dona has a high and stable level of productivity. For 6 years of competitive variety testing the mean productivity of the variety sown in green manure fallow was 9.45 t/ha with the minimum of 6.77 t/ha and the maximum of 11.80 t/ha, compared to the standard variety Ermak with 8.80, 6.06 and 11.21 t/ha, respectively. The variety Rubin Dona sown after various forecrops also demonstrates a reliable and stable productivity increase to the standard, 0.67 t/ha after maize for grain, 0.79 t/ha after peas, 0.62 t/ha after sunflower, 0.77 t/ha after winter wheat. There has been revealed that the advantage of the new variety, which provides high and stable yields, is its high environmental resistance to regional soil and climatic conditions such as drought, low temperatures, spring frosts, diseases, and lodging. The variety has lower indicators of the coefficient of variation, factor of stability (FS), yield range (d) with a high level of realization of productivity potential in comparison with both the standard variety Ermak and the highly productive variety Razdolie, which has a contrasting periods of heading and ripening. The technological and baking properties of the new variety are of high quality and meet the requirements of GOST-9353-2016 referring to the first class. Since 2023, by decision of the State Commission of the Russian Federation for testing and protection of breeding achievements, the variety has been included in the State List of the varieties approved for use in the Central Blackearth (5) and Lower Volga (8) regions.

Hyperbranched anionic surfactant with superwettability and high alkaline resistance from isobutene upgrading

Isobutene, a byproduct of the crude oil catalytic cracking process, is recognized as an attractive feedstock for producing value-added chemicals. Surfactants, conventionally composed of a hydrophobic tail and a hydrophilic head, constitute an indispensable class of versatile consumer chemicals. To date, there have been no effective pathways for upgrading of isobutene to valuable surfactants. In this contribution, we firstly reported a novel hyperbranched anionic surfactant, IB4SO3Na, which not only showed superwettability on various solid surfaces (contact angle < 30°), but also rapidly penetrated textile surfaces (< 0.6 s) and exhibited superior alkaline resistance (aqueous solutions at > 30 g∙L−1 NaOH), outperforming the commercial rapid penetration agent Aerosol-OT (AOT). The hedgehog-like hydrophobic tail, teraisobutylene (IB4), generated from the dimerization of diisobutylene (IB2), endowed the surfactant with superior defoaming properties. Remarkably, fine-tuning the reaction temperature permitted the synthesis of pure IB4 with excellent selectivity (up to 99 %) at − 40 °C, the proportion of which bearing terminal olefin moieties amounted to 61.0 %. In situ Raman spectroscopy revealed that cracking of IB4 can be effectively inhibited at low temperatures. This study provides a universal design strategy for the development of potential highly alkali-resistant penetrants produced from low-cost feedstocks.

High Mortality Rates and Antimicrobial Resistance in Children with Invasive Bacterial Infections in a Tertiary Care Facility in West Africa

Abstract Background Childhood data on infection mortality and antimicrobial resistance in Sub-Saharan Africa are emerging but remain limited. The University of Maryland Center for Vaccine Development (CVD) and CVD-Mali have been conducting a prospective observational study at L’Hopital Gabriel Toure (HGT), a referral hospital in Bamako, Mali, since 2002 to identify causes of invasive bacterial infections (IBI) in children. These data have been used to initiate vaccination programs to decrease the burden of Haemophilus influenzae type b and Streptococcus pneumoniae. Additional demographic and antimicrobial susceptibility data have been collected since 2021, allowing for more detailed resistance and mortality analyses. Methods All children presenting to HGT are screened. Children ages 0-15 years with temperature of at least 39 degrees Celsius and/or suspicion of IBI are eligible. Eligible children have blood cultures collected with additional site-specific cultures when focal infection is suspected. Cultures are performed using the Bactec system; when positive, Gram staining, sub-culturing, and antimicrobial susceptibility testing (by disk diffusion using standard methods) are performed. Organisms thought to be contaminants are excluded. American type culture collection strains are utilized for quality control. Results Between 1/14/2021 and 9/14/2023, 28703 patients were screened. 2156 patients were included. 212 patients (10%) had 235 pathogens isolated. Gram positive organisms were most frequently isolated (N=112), followed by Gram negative Enterobacterales (N=81), non-Enterobacterales Gram negatives (N=36), and yeast (N=6). Staphylococcus aureus was the most frequently isolated Gram positive organism (59 bloodstream isolates, 2 joint isolates, 2 subcutaneous isolates) followed by S.pneumoniae (10 bloodstream isolates, 17 cerebrospinal fluid isolates, 1 joint isolate) and Enterococcus species (16 bloodstream isolates). Klebsiella pneumoniae (28 bloodstream isolates, 2 cerebrospinal fluid isolates) and Escherichia coli (18 bloodstream isolates, 3 cerebrospinal fluid isolates, 2 subcutaneous isolates) were the most frequently isolated Gram negative Enterobacterales, with Pseudomonas species most common among non-Enterobacterales Gram negative organisms (16 bloodstream isolates, 1 cerebrospinal fluid isolate). Mortality rates in both culture-positive and culture-negative patients were high (52% and 28%, respectively), with greater than 50% of deaths occurring within 48 hours in both groups. 88% of Gram negative Enterobacterales were ceftriaxone resistant or intermediate, with 56% ciprofloxacin resistant or intermediate; 55% of isolates were resistant or intermediate to both. 71% of isolates were gentamicin resistant. Imipenem resistance remained low, with 91% of isolates retaining sensitivity. 24% of S. aureus isolates were oxacillin resistant and 34% of isolates were resistant or intermediate to trimethoprim/sulfamethoxazole. 100% of S. aureus isolates tested (14/60) retained sensitivity to clindamycin. Only 54% of pneumococcal isolates had positive oxacillin screens, implying frequent penicillin resistance, and only 60% of enterococcal species were ampicillin sensitive, although 92% retained vancomycin sensitivity. Conclusion We found higher mortality rates in our study than in similar studies; the contribution of issues such as limited access to advanced supportive care and delay in presentation is an area for further study. The high frequency of multidrug-resistant organisms is alarming, suggesting an urgent need to investigate underlying contributing factors, increase access to affordable broad-spectrum antibiotics, and create robust antimicrobial stewardship programs.

Using Thin Ultra-High-Molecular-Weight Polyethylene Coatings to Reduce Friction in Frost-Resistant Rubbers

Frost-resistant rubbers retain their highly elastic properties over a wide temperature range. They are used in various friction units (e.g., seals), but their high friction coefficient and low wear resistance lead to the need for frequent replacement. In this paper, we propose applying thin (several hundred microns) UHMWPE coatings to formed rubber rings. The application technology depends on the required coating thickness. Friction tests of the coatings and pure UHMWPE were performed using the ball-on-disk (unidirectional sliding) scheme for various loads and velocities. In the experiments, the friction coefficients and temperatures near the contact area were determined. Friction tracks were studied using microscopy methods. The sliding contact of the ball and the two-layer material was modeled to obtain the dependences of the deformation component of friction on the sliding velocity for coatings of different thicknesses. UHMWPE is sensitive to frictional heating, so the thermal problem of determining the temperature in the contact area was also solved. It is shown that the minimum friction coefficient occurs for coatings with a thickness of 600 μm. At the same time, in the case of the 300 μm coating, the surface of the friction track is practically no different from the initial one. Thus, the studied combination of polymers provides antifrictional properties and wear resistance to the surface layer while maintaining the damping properties of rubber.

Construction of a 3D spider web structure with spherical Ho2O3 wrapped by carbon nanofibers for high-efficiency microwave absorption and corrosion protection

Reasonable composition control and microstructure design are the effective ways to realize multi-functional high-performance absorbing materials. In this work, a three-dimensional (3D) spider web structure was designed by the electrospinning and high temperature carbonization technology, where Ho2O3 spheres were wrapped by carbon nanofibers. Herein, the spherical Ho2O3 were surrounded by layers of carbon nanofibers (spider silk), which were like the preys inside the spider's web. This unique bionic structure working in conjunction with the tuned components enables the as-prepared composites with improved impedance matching and enhanced loss capacity. The superior electromagnetic wave absorption performance was obtained as the minimum reflection loss of −61.37 dB at 2.90 mm and the maximum effective absorption bandwidth of 6.88 GHz (11.12–18 GHz) at 2.64 mm. At a thickness of 3.44 mm, the effective absorption bandwidth is 4.80 GHz (8–12.80 GHz), covering the entire X-band. At the same time, the composite soaked in the corrosive medium for 7 days owns a low corrosion current density (10−4 ∼10−6 A cm−2) and a high polarization resistance (105∼107 Ω), which exhibits the obvious anticorrosion ability. This work designs a specific spider web structure with high-performance microwave absorption and corrosion protection.

Light and temperature culture conditions impact the metabolome of the cyanobacterium of therapeutic interest Planktothricoides raciborskii PMC 877.14

Cyanobacteria are ancient photosynthetic microorganisms with a long evolutionary history that have adapted to inhabit diverse environments, such as thermal waters and muds. To do so, they are known to produce a wide range of bioactive molecules likely involved in adaptative traits such as high light and/or high temperature resistance mechanisms, which makes them particularly interesting for inclusion in thermal treatments and various therapeutic applications.In this study, the impact of higher temperature and light intensity culture conditions on the metabolome of a promising cyanobacterial strain isolated from the muds of the Balaruc-les-Bains thermal station, Planktothricoides raciborskii PMC 877.14, was investigated through liquid chromatography and mass spectrometry analyses. Statistical analyses of the biological data and molecular network construction allowed for the exploration of potential metabolite induction under different culture conditions, in order to drive the production of specific metabolites aimed at coping with cellular stress. A global shift on intracellular metabolic composition was observed over time with increased biomass production. Higher light intensity was found to stimulate both growth and production of antioxidant and/or photoprotective molecules (such as ergothioneine, mycosporine-like amino acids or carotenoids) while an increase in temperature influenced the higher production of phycobilins (such as phycoerythrin and phycocyanin).These results highlight the importance of culture/environmental conditions in driving intracellular metabolite differentiation and open up new perspectives in selecting of the optimal parameters for the growth and production of bioactive molecules for therapeutic applications in the cyanobacterium P. raciborskii PMC 877.14.

Mechanisms of Controllable Growth and Ohmic Contact of Two-Dimensional Molybdenum Disulfide: Insight from Atomistic Simulations.

ConspectusTwo-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs), in particular molybdenum disulfide (MoS2), have recently attracted huge interest due to their proper bandgap, high mobility at 2D limit, and easy-to-integrate planar structure, which are very promising for extending Moore's law in postsilicon electronics technology. Great effort has been devoted toward such a goal since the demonstration of protype MoS2 devices with high room-temperature on/off current ratios, ultralow standby power consumption, and atomic level scaling capacity down to sub-1-nm technology node. However, there are still several key challenges that need to be addressed prior to the real application of MoS2-based electronics technology. The controllable growth of wafer-scale single-crystal MoS2 on industry-compatible insulating substrates is the prerequisite of application while the currently synthesized MoS2 films mostly are polycrystalline with limited sizes of single-crystal domains and may involve metal substrates. The precise layer-control is also very important for MoS2 growth since its electronic properties are layer-dependent, whereas the layer-by-layer growth of multilayer MoS2 dominated by the van der Waals (vdW) epitaxy leads to poor thickness uniformity and noncontinuously distributed domains. High density up to 1013 cm-2 of sulfur vacancies (SVs) in grown MoS2 can cause unfavorable carrier scatting and electronic properties variations and will inevitably disturb the device performance. The dangling-bond-free surface of MoS2 gives rise to an inherent vdW gap at metal-semiconductor (M-S) contact, which leads to high electrical resistance and poor current-delivery capability at the contact interface and thereby substantially limits the performances of MoS2 devices.In this Account, we briefly review recent experimental and theoretical attempts for addressing the aforementioned challenges and present our own insights from atomistic simulations. We theoretically revealed the vital role of substrate steps for guiding unidirectional nucleation of monolayer MoS2 and uniform nucleation and edge-aligned growth of bilayer MoS2 by advanced simulations. The established thermodynamic mechanisms have successfully directed the experimental works on the controllable growth of 2 in. single-crystal monolayer and centimeter-scale uniform bilayer MoS2. The postgrowth repair mechanism of SV defect in MoS2 via thiol chemistry treatment has been theoretically explored with the consideration of side reaction of surface functionalization to help experimentally reduce SV defect density by 75%. Beyond the atomic level understanding, theoretical simulations proposed the electronic states hybridization mechanism across the semimetal-MoS2 vdW interface, thereby guiding experimental effort for realizing Ohmic contact at the MoS2-Sb(0112) vdW interface with record-low contact resistance.These advances provide a sound basis with an atomic-level understanding for addressing the related issues. However, there are still notable gaps in terms of system size and time scale of dynamics between atomistic simulations and experimental observations for the studies of MoS2 growth and interfaces. The combination of multiscale simulations and artificial intelligence technology is expected to narrow these gaps and provide a more insightful understanding of the controllable growth and interfacial properties modulation of MoS2. We conclude the Account with the standing challenges and outlook on future research directions from the theoretical perspective.

Time-dependent responses and modeling of circular steel tube confined reinforced concrete (STCRC) accounting for partial exposure condition

Circular steel tube confined reinforced concrete (STCRC) columns are becoming increasingly popular in high-rise buildings in China due to their high compressive strength, excellent seismic performance, and high fire resistance. However, the time-dependent behavior has not been well studied for these columns. The time-dependent behavior of STCRC columns is particular, due to the longitudinally partial exposure condition for the concrete core, which is different from either fully exposed members or fully sealed ones. To investigate this difference, long-term experiments with a test duration of 1465 days were conducted on partially exposed circular STCRC columns and the test results were compared against those from fully exposed and fully sealed specimens. With the partial exposure condition accounted for by modifying the notional size h0 of the concrete core, a mathematical expression was then theoretically developed and benchmarked against the test data. Investigation shows that: (1) significant differences exist in the time-dependent deformation between partially exposed, fully exposed, and fully sealed columns; (2) with the modified notional size (defined as the longest path length for the water diffusion), the EC2 model can well predict the time-dependent deformation of partially exposed circular STCRC columns, with a maximum deviation of 7.6 %. The Mean Stress (MS) method is suggested for the conceptual design to achieve safer results.

Investigation of Titanium Nitride as an Effective Interphase for Carbon-Fiber-Reinforced Silicon Carbide Ceramic Matrix Composites.

Ceramic matrix composites (CMCs) have played a significant role in increasing the efficiency of gas turbine engines. CMCs combine the high temperature resistance of ceramics with the high mechanical strength of ceramic fibers into a single unit. Interphase layers are a crucial component in CMCs, as they prevent ceramic fibers from oxidation and introduce strengthening mechanisms into the composite. Hexagonal boron nitride and pyrolytic carbon are the most commonly used interphase layers in the aerospace industry. Other than that, very few materials have been evaluated as interphase layers. In this study, we explore the possibilities of using titanium nitride as an interphase layer in single-tow CMCs (mini composite) representative of a unidirectional composite at a smaller scale. T-300 carbon fibers were coated with TiN by atmospheric pressure chemical vapor infiltration using TiCl4, N2, and H2. The deposition temperature, precursor flow rate ratio, total precursor flow rate, and deposition time were optimized to obtain high-quality coatings. The best coating was produced at 800 °C, 4:1 H2 [TiCl4]/N2 ratio, 125 standard cubic centimeters per minute (N2 + H2 [TiCl4]) total flow precursor flow rate, and 2 h of deposition time. At these conditions, the coatings displayed good fiber coverage, good fiber adhesion, minimum fiber linkage, and minimum surface roughness. There was minimum fiber degradation after TiN coating, with a retention of 95% of the initial Young's modulus and 26% of the ultimate tensile strength of the carbon fiber. Adding the TiN interphase coating to the Cf/SiC CMC increased the ultimate tensile strength of the composite by 1122% and Young's modulus by 150%.

A whole-plant perspective of hydraulic strategy in temperate desert shrub species.

Desert shrubs play a crucial role in controlling desertification and promoting revegetation, but drought often hinders their growth. Investigating the hydraulic strategies of desert shrubs is important to understand their drought adaptation and predict future dynamics under climate change. In this study, we measured the hydraulic-related characteristics of roots, stems, and leaves in 19 desert shrub species from northern China. We aimed to explore the hydraulic coordination and segmentation between different plant organs. The results were as follows (1) Specific root length (SRL) was positively correlated with the water potential inducing a 50% loss in stem hydraulic conductivity (P50stem) and negatively correlated with stem hydraulic safety margin (HSMstem). This suggested that water uptake efficiency of the fine roots was traded off with stem embolism resistance and hydraulic safety. (2) The water potential inducing a 50% loss in leaf hydraulic conductance (P50leaf) was significantly less negative than P50stem, and fine root turgor loss point (TLProot) was significantly less negative than P50stem, indicating a hydraulic segmentation between the main stem and terminal organs. (3) The most negative TLPleaf indicated that leaf wilting occurred after substantial leaf and stem embolism. The high desiccation resistance of the leaves may serve as an important physiological mechanism to increase carbon gain in a relatively brief growth period. In summary, this study elucidated the hydraulic strategies employed by desert shrubs from a whole-plant perspective.

Preparation of molybdenum disulfide/bentonite nanohybrid and its tribological properties as lubricant for water-based drilling fluids

In recent years, with the increase in energy demand and gradual scarcity of medium and shallow oil and gas resources, oil and gas exploration has shifted to special wells such as deep wells, ultra-deep wells, and extended reach wells. These complex wellbore structures inevitably increase the torque and friction between the casing and the drill pipe during drilling, which aggravates friction and wear, and leads to accidents such as drill sticking and drill breakage in severe cases. In this study, molybdenum disulfide/bentonite (MoS2/Bent) nanohybrids as drilling fluid lubricant were synthesized by hydrothermal method using sodium molybdate (Na2MoO4) and thiourea (CH4N2S) as raw materials and bentonite as carrier. The as-synthesized MoS2/Bent nanohybrid was characterized by X-ray powder diffractometer, transmission electron microscopy, Fourier transform infrared spectroscopy, and the high temperature resistance and tribological properties of MoS2/Bent nanohybrid were evaluated in base slurry. The results show that the friction coefficient of MoS2/Bent nanohybrid drilling fluid before aging is reduced by 74 % and the wear rate is reduced by 97 % compared with the base slurry. After high-temperature aging at 240 °C, the friction coefficient is reduced by 77 % and the wear rate is reduced by 90 %. The excellent friction reducing and antiwear performance is attributed to the formation of low shear strength MoS2 deposition film and oxide tribofilm on the surface of the friction pair during the rubbing process.

Effect of Ca addition on structure, phase composition and hardness of Al–6 %Cu–2 %Mn sheet alloy

The Al–Cu–Mn–Ca system was proposed as a bases for the design of new group of heat-resistant alloys which can be used for high-temperature applications instead of the 2219 types industrial alloys. Unlike the latter ones, the new alloys also do not require a full cycle of strengthening heat treatment including solid solution treatment, quenching and aging. The effect of calcium addition in the 1–4 wt% range on the structure, phase composition and hardness after high temperature annealing of the Al–6 %Cu–2 %Mn base sheet alloy has been studied. It has been shown that calcium addition leads to the formation of high-temperature eutectics (614–617 °С) with the participation of the Al27Ca3Cu7 and (Al,Cu)4Ca phases that are capable of spheroidization at high temperature annealing. The ingots of Ca-containing alloys do not require homogenization but have sufficient deformation plasticity at both hot and cold rolling. The structure of the previously unstudied quaternary Al–Cu–Mn–Ca phase diagram in the region of the aluminum corner has been also proposed, according to which it can contain 5 four-phase fields in the solid state with the participation of (Al), binary (Al2Cu, Al4Ca, Al6Mn) and ternary (Al8CaCu4, Al27Ca3Cu7, Al10CaMn2 and Al20Cu2Mn3) phases. Based on the obtained data, the composition Al–6 %Cu–2 %Mn–1 %Ca has been proposed as a basis for the development of a new heat-resistant alloy. It is shown that this alloy superior to industrial 2219 alloy in terms of heat resistance, especially after annealing at 400 °C, when the difference in hardness reaches 32 HV. The high heat resistance of the new wrought alloy originates from the formation of a specific microstructure consisting of fine Ca-containing eutectic inclusions and Al20Cu2Mn3 phase dispersoids with a size of about 100 nm which prevent recrystallization and allow maintaining the fine sub-grained structure.

Synergistic enhancement of chemical and electromagnetic effects in a Ti3C2Tx/AgNPs two-dimensional SERS substrate for ultra-sensitive detection

BackgroundIt is well established that surface-enhanced Raman scattering (SERS) is one of the most commonly used spectral analysis techniques in real-world applications, including chemical and biological sensing, analytical detection, and even forensics. It offers high sensitivity, high resistance to solvents, photobleaching, and limited spectrum bands. In general, SERS is caused by two mechanisms, the electromagnetic enhancement mechanism (EM) and the chemical enhancement mechanism (CM), although the exact mechanism is not yet known. For increased sensitivity, a SERS substrate based on EM coupled with CM is essential. ResultsUsing electrostatic self-assembly, we fabricated many homogeneous hot spots for the substrate by evenly mixing positive charge Ag nanoparticles (AgNPs) with negative charge Ti3C2Tx. In addition, there is a clearly enhanced effect due to the high affinity between the tested molecule and Ti3C2Tx, which facilitates molecule-to-molecule charge transfer. After successfully preparing the Ti3C2Tx/AgNPs substrate, the R6G dye molecule was used to investigate its SERS activity. According to the results, the substrate can reach an enhancement factor of 3.8 × 108. Furthermore, it has been demonstrated that the coupling effect between EM and CM is the main reason for the excellent performance of the Ti3C2Tx/AgNPs composite substrate. Based upon the results of detecting the two biomarkers, adenosine triphosphate and folic acid, the detection limits were determined to be 4.27 × 10−9 M and 7.26 × 10−13 M, respectively. Significance and noveltyTwo-dimensional metal carbide Ti3C2Tx material can be used to obtain CM in surface Raman scattering. It has been demonstrated that the combination of CM and EM with nano-precious metals can produce an extremely sensitive SERS substrate that is dependable and stable. Additionally, the Ti3C2Tx/AgNPs study offers a novel perspective for the advancement of the SERS coupling mechanism in addition to providing direction for realistic detection.

Influence of compliance and resistance of the test lung on the accuracy of the tidal volume delivered by the ventilator

BackgroundLarge variations in respiratory system compliance and resistance may cause the accuracy of tidal volume (VT) delivery beyond the declared range. This study aimed at evaluating the accuracy of VT delivery using a test lung model to simulate pulmonary mechanics under normal or disease conditions.MethodsIn vitro assessment of the VT delivery accuracy was carried out on two commercial ventilators. Measurements of the inspired and expired VT from the ventilator and FlowAnalyser were compared to evaluate the separated and combined influences of compliance and resistance on the delivered VT accuracy. To do this, the errors of five delivered volumes (30 ml, 50 ml, 100 ml, 300 ml, and 500 ml) were checked under 29 test conditions involving a total of 27 combinations of resistance and compliance.ResultsFor the tested ventilator S1 with a flow sensor near the expiratory valve, the average of expired VT errors (ΔVTexp) in three measurements (4 test conditions for each measurement) correlated to test lung compliance (r=-0.96, p = 0.044), and the average of inspired VT errors (ΔVTins) correlated to compliance (r = 0.89, p = 0.106); for the tested ventilator S2 with a flow sensor located at the Y piece, no clear relationship between compliance and ΔVTexp or ΔVTins was found. Furthermore, on two ventilators tested, the current measurements revealed a poor correlation between test lung resistance and ΔVTins or ΔVTexp, and the maximum values of ΔVTexp and ΔVTins correspond to the maximum resistance of 200 cmH2O/(L/s), at which the phenomenon of the flap fluttering in the variable orifice flow senor was observed, and the recorded peak inspiratory pressure (Ppeak) was much higher than the Ppeak estimated by the classical equation of motion. In contrast, at the lower resistance values of 5, 20, 50 and 100 cmH2O/(L/s), the recorded Ppeak was very close to the estimated Ppeak. Overall, the delivered VT errors were in the range of ± 14% on two ventilators studied.ConclusionsDepending on the placement site of the flow sensor in the ventilator circuit, the compliance and resistance of the test lung have different influences on the accuracy of VT delivery, which is further attributed to different fluid dynamics effects of the compliance and resistance. The main influence of compliance is to raise the peak inspiratory pressure Ppeak, thereby increasing the compression volume within the ventilator circuit; whereas a high resistance not only contributes to elevating Ppeak, but more importantly, it governs the gas flow conditions. Ppeak is a critical predictive indicator for the accuracy of the VT delivered by a ventilator.

Evaluating the Effects of Cement Asphalt Emulsion Paste as a Grouting Material on the Fatigue and Thermal Contraction Properties of Semi-Flexible Asphalt composite pavement

Semi-flexible Asphalt (SFA) composite pavement is widely used in pavement engineering for its high load-bearing capacity, enhanced durability, impermeability, and resistance to fuel and oil spillage. This study investigates improving SFA's resistance to cracking by using cement asphalt emulsion paste as a grouting material. SFA specimens were grouted with cement paste (CP) containing 20%, 40%, and 60% asphalt emulsion. These specimens were subjected to indirect tensile strength, resilient modulus, and fatigue tests, along with evaluating thermal contraction behavior using the coefficient of thermal contraction. Results indicated that increasing the asphalt emulsion in CP enhances SFA’s flexibility and ductility but reduces tensile strength and stiffness. Additionally, a mathematical model was developed to predict the resilient modulus from tensile strength tests across temperatures from 5 to 40 °C. The fatigue analysis demonstrated a significant difference in fatigue resistance between SFA and AC16. Incorporating asphalt emulsion also improved SFA's thermal contraction behavior.

Tough and temperature-resistant mask-based separator realized by K-β”-Al2O3 protective layer for stabilizing NaK liquid metal batteries

The development of low-cost, high-temperature-resistant separators is crucial for optimizing the reaction interface and improving the safety performance of liquid NaK metal batteries. This paper presents a novel separator with a solid electrolyte layer, Mask@40 %β-Al2O3, primarily composed of K-β”-Al2O3 known for its exceptional ionic conductivity and high-temperature resistance. Specifically designed for room-temperature liquid NaK metal batteries, the Mask@40 %β-Al2O3 separator effectively transforms the unstable liquid–liquid interface between liquid NaK metal electrodes and traditional organic electrolytes into a stable solid–liquid interface. This transformation prevents short-circuiting caused by area collapse under high-temperature conditions. Moreover, the Bare Mask component can adsorb a conventional organic electrolyte to construct a stable solid–liquid interface on the cathode side, thereby reducing the typically observed high interfacial resistance associated with conventional solid electrolytes. The cost-effective nature and simple preparation process of the Mask@40 %β-Al2O3 separator address cost concerns while presenting an encouraging new direction for applying room-temperature liquid NaK metal batteries in extreme conditions.

Evaluation navigation controlled gate of aging spillway on cavitation damage.

High-speed flow of clean water or water with sediment released from aging spillways may cause abrasion and cavitation on the concrete surface gradually. The occurrence of irregularities on the concrete surface can exacerbate the erosion problem. Which might jeopardize the safety of dams constantly, hence the rehabilitation efforts become urgent tasks in dam safety projects. This study employs a 3D Computational Fluid Dynamics (CFD) model to quantitatively analyze the cavitation risk on the aging concrete surface of the Chay 5 spillway in Ha Giang, Vietnam, under various operation scenarios. There are two standards used to measure cavitation: the cavitation index (σ) which indicates the danger due to the drop of pressure in rapid flow, and the new gasification index (β) which takes into consideration the formation and collapse of bubbles behind asperities. Three extreme flood cases may not result in potential cavitation because both σ and β exceed critical thresholds. Regarding the six controlled gate scenarios with normal water level, the σ profiles are approximated 1,0 showing a low likelihood of cavitation damage while the β values are smaller than 0.8, indicating a considerable risk of cavitation. Besides, the opening height of 100 cm poses the greatest risk of creating severe cavitation erosion in the concave area and slope portion. The flip bucket experienced the most vulnerable cavitation when the opening height is 400 cm. In addition, an approach to spillway surface rehabilitation involving specialized mortars has been presented. For aging conveyance structure, gasification index (β) takes into account irregularities surface, providing a more comprehensive assessment of the likelihood of cavitation damage than cavitation index (σ). After rehabilitation with anti-shrinkage high abrasion resistance mortar, the entire spillway surface is smooth. This allows for reducing the cavitation risk and improvement of life service thereof.