Search Results (22)

In general, graphene is known to be thermally stable. In this study, we analyzed the Raman spectra of graphene prepared on copper (Cu) and nickel (Ni) by chemical vapor deposition (CVD) as well as monolayer and multilayer graphene transferred onto SiO₂ under vacuum heating. We observed a shift in the position of the graphene G peak due to temperature changes for all substrates. For graphene on insulating substrates, the peak position returned to its original position after heating when the substrate returned to room temperature, indicating the thermal and chemical stability of graphene. In contrast, the Raman spectra of graphene on Cu and Ni, which have different carbon solubilities, showed significant shifts and broadening of the G peak as the temperature increased. We also utilized optical microscopy to observe morphological changes during heating, which complemented the Raman spectroscopy analysis. The optical microscopy images obtained in the previous study revealed morphological changes on the graphene surface that correlate with the shifts observed in the Raman spectra, especially in graphene on metal substrates. These combined findings from Raman spectroscopy and optical microscopy could provide insights for optimizing graphene growth processes. In addition, knowledge of the thermal behavior of graphene on insulating substrates could be useful for device construction. Full article

This article introduces a small microwave remote sensing satellite weighing 310 kg, operating in low earth orbit (LEO). It is equipped with an X-band synthetic aperture radar (SAR) antenna, capable of a maximum imaging resolution of 0.6 m. To achieve the objectives of lower cost, reduced weight, minimized power consumption, and enhanced temperature stability, an optimized thermal design method tailored for satellites has been developed, with a particular focus on SAR antennas. The thermal control method of the antenna is closely integrated with structural design, simplifying the thermal design and its assembly process, reducing the resource consumption of thermal control systems. The distribution of thermal interface material (TIM) in the antenna assembly has been carefully calculated, achieving a zero-consumption thermal design for the SAR antenna. And the temperature difference of the entire antennas when powered on and powered off would not exceed 17 °C, meeting the specification requirements. In addition, to ensure the accuracy of antenna pointing, the support plate of antennas requires stable temperature. The layout of the heaters on the board has been optimized, reducing the use of heaters by 30% while ensuring that the temperature variation of the support board remains within 5 °C. Then, an on-orbit thermal simulation analysis of the satellite was conducted to refine the design and verification. Finally, the thermal test of the SAR satellite under vacuum conditions was conducted, involving operating the high-power antenna, verifying that the peak temperature of T/RM is below 29 °C, the temperature fluctuation amplitude during a single imaging task is 10 °C, and the lowest temperature point of the support plate is 16 °C. The results of the thermal simulation and test are highly consistent, verifying the correctness and effectiveness of the thermal design. Full article

(Si/graphite)@C and (Si/graphite/graphene)@C were synthesized by coating asphalt-cracked carbon on the surface of a Si-based precursor by spray drying, followed by heat treatment at 1000 °C under vacuum for 2h. The impact of graphene on the performance of silicon–carbon composite-based anode materials for lithium-ion batteries (LIBs) was investigated. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) images of (Si/graphite/graphene)@C showed that the nano-Si and graphene particles were dispersed on the surface of graphite, and thermogravimetric analysis (TGA) curves indicated that the content of silicon in the (Si/graphite/graphene)@C was 18.91%. More bituminous cracking carbon formed on the surface of the (Si/graphite/graphene)@C due to the large specific surface area of graphene. (Si/Graphite/Graphene)@C delivered first discharge and charge capacities of 860.4 and 782.1 mAh/g, respectively, initial coulombic efficiency (ICE) of 90.9%, and capacity retention of 74.5% after 200 cycles. The addition of graphene effectively improved the cycling performance of the Si-based anode materials, which can be attributed to the reduction of electrochemical polarization due to the good structural stability and high conductivity of graphene. Full article

Sour cherries are a perishable raw material, and their preservation is needed to extend their availability to consumers. Improving drying techniques is desirable to ensure the highest quality of products. This study aimed to determine image textures from color channels R, G, B, L, a, b, X, Y, and Z; color parameters L*, a*, and b*; the color difference (ΔE) of raw materials and dried fruit; and the sensory attributes of dried sour cherry products prepared using an innovative approach. Three sour cherry cultivars, ‘Nefris’, ‘Debreceni Botermo’, and ‘Łutówka’, were used in the experiment. Sour cherries were subjected to freezing and pit removal before drying. The simultaneous osmotic–microwave–vacuum drying was carried out in one process lasting an hour and combining osmotic dehydration using a 40 °Bx sucrose solution and microwave–vacuum drying at microwave powers of 100 W for 900 s, 300 W for 900 s, 250 W for 900 s, and 0 W for stabilization for 900 s and a pressure of 30 ± 2 hPa. After drying, the quality assessment of products was performed using non-destructive image analysis and color measurements, as well as sensory analysis, including non-destructively and destructively assessed attributes. The highest changes in textures occurred for the GHMean (histogram’s mean for color channel G) (from 30.69 to 22.64) and LHMean (histogram’s mean for color channel L) (from 66.93 to 59.07) of images of the cultivar ‘Łutówka’, and the smallest changes were found for the cultivar ‘Nefris’. Drying had a statistically significant effect on the color parameters of the ‘Debreceni Botermo’ and ‘Łutówka’ sour cherries. The value of ΔE was the highest (10.44) for ‘Debreceni Botermo’ and the smallest (1.98) for ‘Nefris’. All cultivars of dried sour cherries had very high values of overall quality, reaching 8.9 for ‘Nefris’ and ‘Debreceni Botermo’ and 8.8 for ‘Łutówka’. The ‘Nefris’ sour cherry was characterized by the highest value of flavor of 9.0. All dried samples were attractive in terms of their external appearance. The sensory parameters related to taste, texture, and crunchiness were also satisfactory. Innovative simultaneous osmotic–microwave–vacuum drying allowed for the obtainment of dried sour cherries with a high quality, including acceptable sensory attributes. Full article

The propagation of Rayleigh waves is usually accompanied by dispersion, which becomes more complex with inherent attenuation. The accurate simulation of Rayleigh waves in attenuation media is crucial for understanding wave mechanisms, layer thickness identification, and parameter inversion. Although the vacuum formalism or stress image method (SIM) combined with the generalized standard linear solid (GSLS) is widely used to implement the numerical simulation of Rayleigh waves in attenuation media, this type of method still has its limitations. First, the GSLS model cannot split the velocity dispersion and amplitude attenuation term, thus limiting its application in the Q-compensated reverse time migration/full waveform inversion. In addition, GSLS-model-based wave equation is usually numerically solved using staggered-grid finite-difference (SGFD) method, which may result in the numerical dispersion due to the harsh stability condition and poses complexity and computational burden. To overcome these issues, we propose a high-accuracy Rayleigh-waves simulation scheme that involves the integration of the fractional viscoelastic wave equation and vacuum formalism. The proposed scheme not only decouples the amplitude attenuation and velocity dispersion but also significantly suppresses the numerical dispersion of Rayleigh waves under the same grid sizes. We first use a homogeneous elastic model to demonstrate the accuracy in comparison with the analytical solutions, and the correctness for a viscoelastic half-space model is verified by comparing the phase velocities with the dispersive images generated by the phase shift transformation. We then simulate several two-dimensional synthetic models to analyze the effectiveness and applicability of the proposed method. The results show that the proposed method uses twice as many spatial step sizes and takes 0.6 times that of the GSLS method (solved by the SGFD method) when achieved at 95% accuracy. Full article

The wood-based panel industry generates a significant amount of solid residues in its production activities, including medium-density fiberboard (MDF) molding manufacturing. These residues consist of fine fibers measuring between 0.15 mm and 1.19 mm in length. A large proportion of them currently needs to be utilized, mainly due to the problem of excessive accumulation. They can be reused as raw material for manufacturing new products by adopting a circular economy approach. Their thermal properties can also be enhanced by impregnating them with phase change materials (PCMs). This research aims to develop a process for impregnating MDF panel residues (R) with PCMs to obtain shape-stabilized compounds capable of storing thermal energy. Three different commercially available PCMs were used. They were incorporated in the MDF residues by vacuum impregnation. The morphology, chemical structure, thermal stability, and phase change properties of the compounds obtained were studied by scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectrometry, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC), respectively. The SEM images indicated the PCM filled the empty spaces in the porous surface of the residue fibers to form shape-stabilized compounds. The FTIR spectrometry results indicated the compounds still exhibited characteristic peaks corresponding to both the MDF residues and the PCMs. No chemical reaction was observed between the two components. Moreover, according to the TGA results, the compounds produced exhibit high thermal stability. The R+PCM1 compound had the highest latent heat capacity of all the compounds developed in this study, reaching a maximum of 57.8 J⋅g⁻¹, and a phase change temperature comparable to that of PCM1. This better thermal performance could be attributed to the compounds having a higher encapsulation ratio (31.4%) than the other compounds developed. Furthermore, the R+PCM1 compound had an absorption capacity of 142.8%. This study, therefore, unveiled a promising alternative for storing thermal energy and valorizing solid MDF residues. Full article

Due to the excellent properties of Ti (C,N)-based ceramics, such as high hardness, excellent wear resistance, exceptional thermal deformation resistance, and sound chemical stability, they have been widely used in cutting tools or molds. Thus, revealing their tribological behavior against hard materials is of great significance. Some studies have reported the tribological behavior of Ti(C,N)-based cermets and hard cermets, but so far, the effects of Mo₂C additions on the frictional properties of Ti(C,N)-based cermets are still unclear. In this study, Ti(C,N)-10WC-1Cr₃C₂-5Co-10Ni-x Mo₂C cermets (x = 4, 6, 8, 10 and 12 wt.%) were sintered using a vacuum hot-pressing furnace. Furthermore, the core–rim morphologies of the sintered samples were observed in SEM images. Then, the wear resistance of the cermets was studied against a Si₃N₄ ball at a 50 N load using the fretting wear test. Finally, the wear mechanism was characterized using a combination of SEM, EDS and XPS. The experimental results indicated that the wear mechanisms of the cermets were mainly abrasive wear, adhesive wear, and the formation of an oxide film. As the content of Mo₂C increased from 4 wt.% to 12 wt.%, the friction coefficient and wear volume had a variation law of first decreasing and then decreasing, and reached minimum values at 6 wt.% and 12 wt.%, and the lowest friction coefficient and wear rate were 0.49 and 0.9 × 10⁻⁶ mm³/Nm, respectively. The 6 wt.% Mo₂C greatly improved the hardness and fracture toughness of the cermet, while the 12 wt.% Mo₂C promoted the formation of an oxide film and protected the friction surface. The cermet with 6 wt.% Mo₂C is recommended because it has comprehensive advantages in terms of its mechanical properties, tribological properties, and cost. Full article

This paper presents an investigation into the plume characteristics of composite propellants fabricated by polytetrafluoroethylene (PTFE) filled with different carbon additives (nano-carbon powder, graphite, and graphene) under laser irradiation in a vacuum environment. The dynamic plumes generated by the laser ablation of different modified propellant samples were captured using a high-speed camera, and the feature parameters of the plumes were extracted by image processing. The results indicated that doping carbon particles in PTFE enhanced the quality of the plasma plumes. The plume area increased up to a certain value and then stabilized, while end of plume clusters remained for a short time. Further analysis revealed that the propellant sample doped with graphene exhibited the maximum plume length and expansion rate, whereas the propellant sample doped with nano-carbon demonstrated the largest plume area. Moreover, a higher graphene doping ratio promoted greater plume length, expansion speed, and plume area. However, when the doping ratio exceeded 3%, the gain of the plume parameters gradually became saturated, and the optimal doping ratio appeared to be 5%. Full article

The search for materials for a new generation of wound coatings is important due to the increase in antibiotic-resistant microorganisms and the number of patients with untreatable chronic purulent wounds. Metal nanoparticles, specifically silver nanoparticles, have antimicrobial activity and do not induce known bacterial resistance. To obtain new Ag-containing nanocomposites, type I collagen was extracted by an enzyme–acid method from cattle tendons. Silver nanoparticles were obtained by an environmentally safe method, metal-vapor synthesis (MVS), which enables obtaining metal nanoparticles without impurities. For this, metal vapors were cocondensed in a vacuum of 10⁻² Pa on the walls of a quartz reactor cooled to 77 K using acetone as an organic dispersion medium. The composition of the collagen surface was determined by XPS using the spectra of C1s, N1s, and O1s. The presence of a peak with a binding energy of approximately 368.57 eV in the Ag 3d_5/2 spectrum indicates the state of Ag⁰ silver atoms in the nanocomposite. SEM images showed that collagen contributes to the effective stabilization of Ag nanoparticles with an average size of 13.0 ± 3.5 nm. It was found that collagen is non-toxic and biocompatible with skin cells and fibroblasts. The collagen–Ag nanoparticle nanocomposites exhibited antimicrobial activity against bacteria Bacillus subtilis, Escherichia coli, and fungi Aspergillus niger. Full article

(1) Introduction. The problem that limits the intraoperative use of OCTA for the intestinal circulation diagnostics is the low informative value of OCTA images containing too many motion artifacts. The aim of this study is to evaluate the efficiency and safety of the developed unit for the prevention of the appearance of motion artifacts in the OCTA images of the intestine in both open and laparoscopic surgery in the experiment; (2) Methods. A high-speed spectral-domain multimodal optical coherence tomograph (IAP RAS, Russia) operating at a wavelength of 1310 nm with a spectral width of 100 μm and a power of 2 mW was used. The developed unit was tested in two groups of experimental animals—on minipigs (group I, n = 10, open abdomen) and on rabbits (group II, n = 10, laparoscopy). Acute mesenteric ischemia was modeled and then 1 h later the small intestine underwent OCTA evaluation. A total of 400 OCTA images of the intact and ischemic small intestine were obtained and analyzed. The quality of the obtained OCTA images was evaluated based on the score proposed in 2020 by the group of Magnin M. (3) Results. Without stabilization, OCTA images of the intestine tissues were informative only in 32–44% of cases in open surgery and in 14–22% of cases in laparoscopic surgery. A vacuum bowel stabilizer with a pressure deficit of 22–25 mm Hg significantly reduced the number of motion artifacts. As a result, the proportion of informative OCTA images in open surgery increased up to 86.5% (Χ² = 200.2, p = 0.001), and in laparoscopy up to 60% (Χ² = 148.3, p = 0.001). (4) Conclusions. The used vacuum tissue stabilizer enabled a significant increase in the proportion of informative OCTA images by significantly reducing the motion artifacts. Full article

New hybrid materials based on Ag nanoparticles stabilized by a polyaminopropylalkoxysiloxane hyperbranched polymer matrix were prepared. The Ag nanoparticles were synthesized in 2-propanol by metal vapor synthesis (MVS) and incorporated into the polymer matrix using metal-containing organosol. MVS is based on the interaction of extremely reactive atomic metals formed by evaporation in high vacuum (10⁻⁴–10⁻⁵ Torr) with organic substances during their co-condensation on the cooled walls of a reaction vessel. Polyaminopropylsiloxanes with hyperbranched molecular architectures were obtained in the process of heterofunctional polycondensation of the corresponding AB₂-type monosodiumoxoorganodialkoxysilanes derived from the commercially available aminopropyltrialkoxysilanes. The nanocomposites were characterized using transmission (TEM) and scanning (SEM) electron microscopy, X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (PXRD) and Fourier-transform infrared spectroscopy (FTIR). TEM images show that Ag nanoparticles stabilized in the polymer matrix have an average size of 5.3 nm. In the Ag-containing composite, the metal nanoparticles have a “core-shell” structure, in which the “core” and “shell” represent the M⁰ and M^δ+ states, respectively. Nanocomposites based on silver nanoparticles stabilized with amine-containing polyorganosiloxane polymers showed antimicrobial activity against Bacillus subtilis and Escherichia coli. Full article

Terahertz imaging has attracted significant interest for its applications in noninvasive medical diagnosis, security systems, and industrial inspections. Superconducting bolometers are one of the promising technologies of ultra-sensitive terahertz detection. Here, we present THz images captured by a low-cost superconducting transition-edge detector. The sensing element of the detector is a meander line patterned ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\mathrm{x}}$ (YBCO) thin film realizing monolithically the absorber and thermometer of the detector. A total of 400 nm YBCO film is deposited on Yttrium-stabilized Zirconia substrate by the metal-organic deposition method which is well-known as an economic and scalable chemical, vacuum-free technique. The meander line pattern consists of 15 series connected parallel lines with a length of 1.5 mm and a width of 50 micrometers. This pattern has shown a significant response to the 0.1 THz equivalents to 3 mm wavelength radiation without any coupled antenna or separate absorber that may reduce the detection speed. The voltage response amplitude of the fabricated detector to 0.1 THz radiation at different modulation frequencies is measured and the detector is utilized for imaging concealed objects including cigarettes and metallic items. Full article

Polyethylene glycol (PEG) non-covalent-functionalized multi-walled carbon nanotubes (MWCNT) membrane were prepared by vacuum filtration. The dispersion and stability of MWCNT non-covalent functionalized with PEG were all improved. TEM characterization and XPS quantitative analysis proved that the use of PEG to non-covalent functionalize MWCNT was successful. SEM image analysis confirmed that the pore size of PEG–MWCNT membrane was more concentrated and distributed in a narrower range of diameter. Contact angle measurement demonstrated that PEG non-covalent functionalization greatly enhanced the hydrophilicity of MWCNT membranes. The results of pure water flux showed that the PEG–MWCNT membranes could be categorized into low pressure membrane. PEG-MWCNT membrane had a better effect on the removal of humic acid (HA) and a lower TMP growth rate compared with a commercial 0.01-μm PVDF ultrafiltration membrane. During the filtration of bovine serum albumin (BSA), the antifouling ability of PEG-MWCNT membranes were obviously better than the raw MWCNT membranes. The TMP recovery rate of PEG–MWCNT membrane after cross flushing was 79.4%, while that of raw MWCNT–_COOH and MWCNT membrane were only 14.9% and 28.3%, respectively. PEG non-covalent functionalization improved the antifouling ability of the raw MWCNT membranes and reduced the irreversible fouling, which effectively prolonged the service life of MWCNT membrane. Full article

Titanium carbide (TiC) thin films were prepared by non-reactive simultaneous double magnetron sputtering. After deposition, all samples were annealed at different temperatures under high-vacuum conditions. This paper mainly discusses the influence of deposition methods and annealing temperatures on microstructure, surface topography, bonding states and electrical resistivity of TiC films. XRD (X-ray diffraction) results show that TiC thin films can still form crystals without annealing, and the crystallinity of thin films is improved after annealing. The estimated grain size of the TiC films varies from 8.5 nm to 14.7 nm with annealing temperature. It can be seen from SEM (scanning electron microscope) images that surfaces of the films are composed of irregular particles, and when the temperature reaches to 800 °C, the shape of the particles becomes spherical. Growth rate of film is about 30.8 nm/min. Oxygen-related peaks were observed in XPS (X-ray photoelectron spectroscopy) spectra, which is due to the absorption of oxygen atoms on the surface of the film when exposed to air. Raman spectra confirm the formation of TiC crystals and amorphous states of carbon. Resistivity of TiC films decreases monotonically from 666.73 to 86.01 μΩ·cm with the increase in annealing temperature. In brief, the TiC thin films prepared in this study show good crystallinity, thermal stability and low resistivity, which can meet the requirements of metal gate applications. Full article

Arc faults induced by residential low-voltage distribution network lines are still one of the main causes of residential fires. When a series arc fault occurs on the line, the value of the fault current in the circuit is limited by the load. Traditional circuit protection devices cannot detect series arcs and generate a trip signal to implement protection. This paper proposes a novel high-frequency coupling sensor for extracting the features of low-voltage series arc faults. This sensor is used to collect the high-frequency feature signals of various loads in series arc state and normal working state. The signal will be transformed into two-dimensional feature gray images according to the temporal-domain sequence. A neural network with a three-layer structure based on convolution neural network is designed, trained and tested using the various typical loads’ arc states and normal states data sets composed of these images. This detection method can simultaneously accurately identify series arc, as well as the load type. Seven different domestic appliances were selected for experimental verification, including a desktop computer, vacuum cleaner, induction cooker, fluorescent lamp, dimmer, heater and electric drill. Then, the stability and universality of the detection algorithm is also verified by using electronic load with adjustable power factor and peak factor. The experimental results show that the designed sensor has the advantages of simple structure and wide frequency response range. The detection algorithm comparison confirms that the classification accuracy of the seven domestic appliances’ work states in the fourteen categories could reach 98.36%. The adjustable load in the two categories could reach above 99%. The feasibility of hardware implementation based on FPGA of this method is also evaluated. Full article