Search Results (443)

In this paper, we study the conformal symmetry for locally rotationally symmetric Bianchi type I space-time. New exact conformal solutions of Einstein’s field equations for this space-time were obtained. The space-time geometry of these solutions is found to be non-vacuum, conformally flat, and shear-free. We show that in order for LRS Bianchi type I space-time to admit a conformal vector field it must reduce to the FRW space-time. Some physical and kinematic properties of the obtained conformal solutions are also discussed. Full article

This paper studies the effect of reversible hydrogen alloying of the TC4 alloy on the microstructure, phase composition, and mechanical properties before and after equal-channel angular pressing. It is shown that the introduction of 0.3% hydrogen followed by quenching from a temperature of 850 °C leads to the formation of a thin-plate α″-martensite, which made it possible to implement 6 passes (ε ~ 4.2) of pressing at 600 °C. As a result of the deformation of the TC4-H alloy and subsequent thermal vacuum treatment to remove hydrogen, an ultrafine-grained structure with an average size of the α-phase of 0.15 μm was formed, which led to strengthening of the alloy to 1490 MPa with a relative elongation of about 5% at room temperature. The reasons for a more significant refinement of the grain/subgrain structure and an increase in the tensile strength of the hydrogenated alloy after equal-channel angular pressing in comparison with hydrogen-free TC4 alloy are discussed. Full article

Splashed droplets in the vacuum chamber play an important role in decarburization and degassing in Ruhrstahl–Heraeus (RH), but the scholars do not pay attention to the behaviors of splashed droplets. Thus, it is necessary to propose a new method to investigate the splashed droplets. A Euler–Euler model and the inter-phase momentum transfer are applied to investigate the interaction between the molten steel and the bubbles, and the gas domain in the vacuum chamber is included in the computational domain in order to describe the movement of the splashed droplets. Numerical results show that the flow field predicted by Euler–Euler model agrees well with the experimental data. There is a higher gas volume fraction near the up-snorkel wall, the “fountain” formed by the upward flow from the up-snorkel exceeds 0.1 m above the free surface, and the center of the vortex between the upward stream and the downward stream is closer to the upward stream in the vacuum chamber. Full article

This study systematically investigated the evolution of color values and the reaction kinetics of the Maillard reaction in membrane-clarified sugarcane juice during the vacuum evaporation process, providing a theoretical basis for pigment regulation in white sugar production. Content changes in the reactants (sucrose, glucose, fructose, and free amino acids), the precursors of melanoidins including 3-deoxyglucosone, 5-hydroxymethylfurfural, glyoxal, methylglyoxal, carboxymethyl lysine, and melanoidin, were monitored during the thermal processing of membrane-clarified sugarcane juice (MCSJ), and the reaction mechanism was investigated via kinetic modeling. The zero-level, first-level, and second-level kinetic models could represent the change in L* and b*, and the zero-level kinetic model best fit the change in a* and ΔE*. The multi-response kinetics revealed that the main pathway of melanoidins in MCSJ model systems was that glucose and fructose were mutually isomerized into 1,2-enediol to generate 3-DG and then degraded to produce 5-HMF. Subsequently, 5-HMF further reacted to produce melanoidins. Full article

Conventional fabrication of high-efficiency organic solar cells (OSCs) predominantly relies on vacuum-evaporated metal top electrodes such as Ag and Al, which hinder large-scale industrial production. Gallium-based liquid metals (GaLMs), particularly the eutectic gallium–indium alloy (EGaIn), represent promising candidates to conventional vacuum-evaporated metal top electrodes due to their excellent printability and high electrical conductivity. In this study, we fabricated vacuum-free OSCs based on GaLM electrodes (Ga, EGaIn, and Galinstan) and analyzed the device performances. Rigid devices with EGaIn electrodes achieved a champion power conversion efficiency (PCE) of 15.6%. Remarkably, all-solution-processed ultrathin flexible devices employing silver nanowire (AgNW) bottom electrodes in combination with EGaIn top electrodes achieved a PCE of 13.8% while maintaining 83.4% of their initial performance after 100 compression–tension cycles (at 30% strain). This work highlights the potential of GaLMs as cost-effective, scalable, and high-performance top electrodes for next-generation flexible photovoltaic devices, paving the way for their industrial adoption. Full article

Background/Objective: Early pregnancy loss is often caused by chromosomal abnormalities, necessitating accurate diagnostic tools. While product of conception (POC) chromosomal testing is commonly used, it can be limited by culture failure or an inability to obtain fetal tissue due to spontaneous expulsion. Cell-free fetal DNA (cff DNA) analysis provides a non-invasive alternative; however, its effectiveness in early pregnancy loss, particularly in cases where fetal components are still minimal, has not been fully established. The objective of this study was to evaluate the accuracy of pre- and postoperative cff DNA analysis for detecting fetal aneuploidy by comparing the results to those of POC chromosomal testing. Methods: In this single-center prospective cohort study, 50 women undergoing manual vacuum aspiration for pregnancy loss before 12 weeks of gestation were enrolled (February 2022–December 2024). Cff DNA analysis was performed on maternal blood samples collected pre- and postoperatively. The primary outcome was concordance between the cff DNA and POC results. Sensitivity, specificity, and factors affecting concordance were also assessed. Results: Eight participants were excluded due to unsuccessful POC culture (n = 3), suspected maternal tissue contamination in the POC sample (n = 1), mosaicism (n = 3), or triploidy (n = 1), resulting in 42 evaluable cases. Preoperative cff DNA analysis showed 88.1% concordance with POC (sensitivity 86.4% and specificity 90.0%). Postoperative analysis showed 78.6% concordance (sensitivity 72.7% and specificity 85.0%). Conclusions: The Cff DNA analysis of preoperative and postoperative maternal blood samples showed generally good concordance with conventional POC chromosomal testing in detecting fetal aneuploidy in early pregnancy loss. Full article

Variable stiffness actuators (VSAs) have attracted considerable attention in wearable robotics and soft exoskeletons due to their ability to adapt to various load conditions. This study presents a modular design for VSAs that incorporates a chain mail structure with various link topologies, allowing for a reconfiguration of stiffness. The proposed VSA consists of three main parts: the vacuum chamber, the VSA actuator, and the chain mail structure. The VSA fabrication process was carried out in five stages: (1) mold fabrication by 3D FDM printing, incorporating a film of oil to facilitate easy demolding; (2) mold preparation using silicone, with a precise ratio of 1:1 weight-based mixture to optimize material utilization; (3) silicone pouring into molds while applying vibration to eliminate air bubbles; (4) curing for four hours to achieve optimal mechanical properties; and (5) careful demolding to prevent damage. Experimental tests were conducted to characterize the stiffness of actuators with different chain mail fabric configurations, using an experimental setup designed to securely fix the actuator and accurately measure the pneumatic pressure and the angle of deformation after applying weights at its end. The European 6-in-1 and rounded square configurations were shown to be the most effective, increasing stiffness up to 382% compared to the chain mail-free configuration, highlighting the positive impact of these structural designs. Full article

Fuel cells, propulsion systems, and reaction control systems (RCSs) are just a few of the space applications that depend on pressure vessels (PVs) to safely hold high-pressure fluids while enduring extreme environmental conditions both during launch and in orbit. Under these challenging circumstances, PVs must be lightweight while retaining structural integrity in order to increase the efficiency and lower the launch costs. PVs have significant challenges in space conditions, such as extreme vibrations during launch, the complete vacuum of space, and sudden temperature changes based on their location within the satellite and orbit types. Determining the operational temperature limits and endurance of PVs in space applications requires assessing the combined effects of these factors. As the main propellant for satellites and rockets, hydrogen has great promise for use in future space missions. This study aimed to assess the structural integrity and determine the thermal operating limits of different types of hydrogen pressure vessels using finite element analysis (FEA) with Ansys 2019 R3 Workbench. The impact of extreme space conditions on the performances of various kinds of hydrogen pressure vessels was analyzed numerically in this work. This study determined the safe operating temperature ranges for Type 4, Type 3, and Type 1 PVs at an operating hydrogen storage pressure of 35 MPa in an absolute vacuum. Additionally, the dynamic performance was assessed through modal and random vibration analyses. Various aspects of Ansys Workbench were explored, including the influence of the mesh element size, composite modeling methods, and their combined impact on the result accuracy. In terms of the survival temperature limits, the Type 4 PVs, which consisted of a Nylon 6 liner and a carbon fiber-reinforced epoxy (CFRE) prepreg composite shell, offered the optimal balance between the weight (56.2 kg) and a relatively narrow operating temperature range of 10–100 °C. The Type 3 PVs, which featured an Aluminum 6061-T6 liner, provided a broader operational temperature range of 0–145 °C but at a higher weight of 63.7 kg. Meanwhile, the Type 1 PVs demonstrated a superior cryogenic performance, with an operating range of −55–54 °C, though they were nearly twice as heavy as the Type 4 PVs, with a weight of 106 kg. The absolute vacuum environment had a negligible effect on the mechanical performance of all the PVs. Additionally, all the analyzed PV types maintained structural integrity and safety under launch-induced vibration loads. This study provided critical insights for selecting the most suitable pressure vessel type for space applications by considering operational temperature constraints and weight limitations, thereby ensuring an optimal mechanical–thermal performance and structural efficiency. Full article

Sea cucumbers are widely consumed as a delicacy or in eastern medicine across many Asian countries. Due to the depletion of traditional stocks, new species are increasingly harvested, including the Atlantic sea cucumber (Cucumaria frondosa), the most abundant, cold-water species found in the North Atlantic. This species is harvested in NAFO subdivision 3Ps off the south coast of Newfoundland and Labrador, Canada. As part of their respiration, stress response, and locomotion, sea cucumbers draw and retain oxygenated water within their body cavity, resulting in significant water content at landing. Historically, Fisheries and Oceans Canada (DFO) have applied a 23% deduction to the landed weight to account for this water retention. To validate this deduction, the authors conducted experiments across thirteen sampling events in 2019 and 2020. Randomized samples were collected during offloading and were categorized into three sizes of bin—small (x ≤ 150 g), medium (150 g < x ≤ 250 g), and large (x > 250 g)—and water loss was measured. Water loss was analyzed in relation to multiple factors, including processor, unloading method, year, license, month, fishing area, hold location, size, and processing method. Key findings included the following: (a) sea cucumbers typically contained more than 23% free water; (b) large and medium-sized specimens, which dominated landings, retained more free water; (c) water loss was highest for the samples collected from the top of the hold; (d) the unloading method influenced free water retention, as did the processing method used to cut the sea cucumbers; (e) license, processor, and fishing area had strong collinearity with other factors or were not found to be statistically significant; and (f) water loss appeared higher in 2020 than 2019, largely due to the increased use of vacuum transfer methods. Based on these findings, DFO revised the water retention allowance to 34%. Full article

High-purity aluminum is widely used in metallurgy, microelectronics and chemical synthesis. In this work, the method of carbothermic reduction of aluminum powder in a microwave plasma discharge with the formation of valuable organic products such as synthesis gas, acetylene and benzene was used. Al powder was studied by inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy (SEM) and powder X-ray diffraction (XRD). The yield of by-products was studied by gas chromatography equipped with a mass spectrometer, as well as optical emission spectroscopy of plasma discharge. High-purity aluminum powder reduced with the plasma was used to synthesize oxygen-free trimethylaluminum (TMA). For the first time, TMA was synthesized in one vacuum cycle without the system depressurizing to improve the purity of the final product. Trimethylaluminum was analyzed by gas chromatography, which confirmed that the main substance is ≥99.99% pure. Gas chromatography with a mass spectrometer was used to determine by-products and residual reaction products. Additionally, ICP-MS was used to confirm trace metal concentrations, achieving the 7N standard for ultra-high-purity materials. Full article

The discontinuation of commercially available saline and hypertonic saline wound dressings for the veterinary market has restricted options available to veterinary practitioners treating contaminated and infected wounds. Clinicians may manufacture their own homemade solutions in clinics or field settings to treat equine or livestock species; however, information is limited on whether autoclave sterilization is necessary or sufficient to eliminate bacterial growth in isotonic and concentrated salt solutions and how long they may subsequently be stored prior to use. The purpose of this study was to assess sterility of saline (0.9%) and hypertonic saline (20%) solutions manufactured three ways (1—autoclaved glass bottle that was autoclaved again following solution preparation; 2—autoclaved glass bottle, not autoclaved again following preparation; 3—non-autoclaved plastic bottle, not autoclaved following preparation). Solutions were stored two different ways (1—solution in sealed bottle or 2—soaked gauze in vacuum-sealed plastic packets). Products were assessed for bacterial growth at four time points (baseline, one week, one month, six months). At each time point, samples of each solution were plated on Luria–Bertani (LB) agar plates and assessed for bacterial growth at 24 h. Vacuum-sealed soaked gauze was placed in antibiotic-free growth media for 24 h, and then media were plated on LB agar plates and assessed for bacterial growth at 24 h. If bacterial growth was detected, qualitative culture with sensitivity was performed to identify bacterial isolates. No bacterial growth was detected in stored solutions for any preparation method, concentration or time point assessed. Bacterial growth was detected from 0.9% saline-soaked gauze at 1 week, 1 month and 6 months in all container types for at least one time point. Bacterial culture revealed Ralstonia, Bacillus, Sphingomonas and Staphylococcus species. Environmental controls (water, containers, salt, biosafety cabinet and benchtop) were submitted for culture to identify the source of contamination, yielding light mixed growth from tap water and no growth from any other locations. These findings provide clinicians with practical information to guide preparation and storage of homemade saline-based products for wound care. Full article

There is evidence that the properties of hadrons are modified in a nuclear medium. Information about the medium modifications of the internal structure of hadrons is fundamental for the study of dense nuclear matter and high-energy processes, including heavy-ion and nucleus–nucleus collisions. At the moment, however, empirical information about medium modifications of hadrons is limited; therefore, theoretical studies are essential for progress in the field. In the present work, we review theoretical studies of the electromagnetic and axial form factors of octet baryons in symmetric nuclear matter. The calculations are based on a model that takes into account the degrees of freedom revealed in experimental studies of low and intermediate square transfer momentum $q^2=-Q^2$: valence quarks and meson cloud excitations of baryon cores. The formalism combines a covariant constituent quark model, developed for a free space (vacuum) with the quark–meson coupling model for extension to the nuclear medium. We conclude that the nuclear medium modifies the baryon properties differently according to the flavor content of the baryons and the medium density. The effects of the medium increase with density and are stronger (quenched or enhanced) for light baryons than for heavy baryons. In particular, the in-medium neutrino–nucleon and antineutrino–nucleon cross-sections are reduced compared to the values in free space. The proposed formalism can be extended to densities above the normal nuclear density and applied to neutrino–hyperon and antineutrino–hyperon scattering in dense nuclear matter. Full article

In this study, the compositional shifts in free and bound phenolic compounds of Morinda citrifolia L. (Noni) processed by different drying methods were investigated. Twenty-seven phenolic compounds, predominantly rutin and quinic acid, were discovered in fresh Noni fruit. Vacuum freeze-drying retained the highest free phenolic content, with rutin (1809.83 mg/kg DW) and quinic acid (198.72 mg/kg DW) as the primary constituents, while bound phenolics were dominated by benzoic acid (35.56 mg/kg DW). Hot-air drying reduced the free phenolics by 51.59% (80% methanol) and the bound phenolics (base hydrolysis) by 35.55%, with a significant degradation of rutin and quinic acid. Microwave drying similarly decreased the free phenolics, though the caffeic acid increased to 46.45 mg/kg DW due to the thermal stability. Bound phenolics showed the highest content (alkaline hydrolysis) in fresh fruits, primarily benzoic acid (220.67 mg/kg DW) and rutin (77.02 mg/kg DW), surpassing the acid/enzyme methods. While vacuum freeze-drying effectively preserved the free phenolics, thermal methods (hot-air/microwave drying) promoted the release of quercetin (free phenols) and 3,4-dihydroxybenzoic acid (bound phenols). The findings of this study elucidate the species-specific compositional dynamics of phenolic compounds under different drying regimes, while providing quantitative guidelines for advancing the understanding of the underlying health-promoting phytochemical profiles of Noni. Full article

It has been shown that at the present stage of the evolution of the universe, cosmological acceleration is an inevitable kinematical consequence of quantum theory in semiclassical approximation. Quantum theory does not involve such classical concepts as Minkowski or de Sitter spaces. In classical theory, when choosing Minkowski space, a vacuum catastrophe occurs, while when choosing de Sitter space, the value of the cosmological constant can be arbitrary. On the contrary, in quantum theory, there is no uncertainties in view of the following: (1) the de Sitter algebra is the most general ten-dimensional Lie algebra; (2) the Poincare algebra is a special degenerate case of the de Sitter algebra in the limit $R\to \infty$ where R is the contraction parameter for the transition from the de Sitter to the Poincare algebra and R has nothing to do with the radius of de Sitter space; (3) R is fundamental to the same extent as c and ℏ: c is the contraction parameter for the transition from the Poincare to the Galilean algebra and ℏ is the contraction parameter for the transition from quantum to classical theory; (4) as a consequence, the question (why the quantities (c, ℏ, R) have the values which they actually have) does not arise. The solution to the problem of cosmological acceleration follows on from the results of irreducible representations of the de Sitter algebra. This solution is free of uncertainties and does not involve dark energy, quintessence, and other exotic mechanisms, the physical meaning of which is a mystery. Full article

Sungkai leaves were selected due to their herbal medicine prevalence and documented biological activities. This study explores the immunomodulatory potential of kaempferol isolated from Sungkai (Peronema canescens Jack.) through a combination of in silico and in vitro methods. P. canescens leaves were extracted with ethanol using maceration, followed by fractionation with n-hexane, ethyl acetate, and water using a separatory funnel. Among all the fractions, the ethyl acetate fraction demonstrated the strongest inhibitory effect on IL-6 (Interleukin 6) expression, leading to further separation for the enhanced analysis of its activity. The resulting sub-fractions were purified by vacuum liquid chromatography with n-hexane and ethyl acetate gradient. Sub-fraction E was isolated through preparative thin-layer chromatography to obtain a pure compound identified as kaempferol using UV, FTIR, MS, and NMR analyses. The isolated kaempferol was then evaluated by molecular docking and molecular dynamics simulations, employing MM-PBSA (Molecular Mechanics Poisson–Boltzmann Surface Area) for binding affinity calculations. Kaempferol showed a binding affinity (ΔG) of −5.98 kcal/mol, slightly stronger than TLA (tartaric acid) (−5.90 kcal/mol). Key interactions with amino acid residues, such as Gln175, Arg182, and Arg179, were observed. Additionally, molecular dynamics simulation demonstrated that kaempferol exhibited better stability than TLA between 15 ns and 100 ns. The MM-PBSA analysis showed that kaempferol has strong van der Waals (−17.02 kcal/mol) and electrostatic interactions (−293.16 kcal/mol), with binding free energy (−17.85 kcal/mol) significantly stronger than TLA (−1.00 kcal/mol). This stability, combined with its ability to reduce IL-6 expression in vitro, highlights kaempferol’s immunomodulatory potential. Full article