Search Results (167)

University CubeSat programs are often conducted under severe constraints in budget, personnel, schedule, and knowledge continuity, while still requiring sufficient verification to support mission success. This paper presents the verification, testing, on-orbit operation, and anomaly analysis of COSMIC, a 3U university CubeSat developed by Yonsei University in less than eleven months from project kickoff to launch. COSMIC adopted a protoflight model approach, prioritized commercial off-the-shelf components with flight heritage and prior laboratory experience, and concentrated limited resources on subsystem, FlatSat, system-level, environmental, communication, and scenario-based testing. The test program is reviewed against the subsequent on-orbit results to identify which verification activities contributed to anomaly prevention, fault isolation, and recovery. The results show that system-level integration testing, thermal vacuum cycle testing, and scenario testing were particularly effective in revealing interface, software, and deployment-related issues before launch and in supporting early orbit recovery. However, the mission also exposed limitations in recovery-logic verification, long-duration software testing, communication robustness, and independent reset paths. Based on these findings, practical recommendations are derived for resource-constrained university CubeSat teams seeking to tailor verification activities without simply reducing test rigor. Full article

The reliable joining of graphite and Cu holds significant promise for applications in electronic heat dissipation and sliding electrical contacts. However, the substantial differences in their physicochemical properties, poor wettability, and mismatch in coefficients of thermal expansion often result in low joint strength. In this study, a two-step joining strategy combines surface modification with low-temperature sintering, and this is proposed for fabrication of Cu/graphite joints. First, the graphite surface is modified using an AgCuTi active filler alloy under vacuum conditions. Ti preferentially segregates at and reacts with the graphite interface, leading to the formation of an Ag-Cu eutectic modified layer on the graphite surface. Subsequently, low-temperature joining of the modified graphite to a Cu substrate is achieved via a hot-pressing sintering process using a Ag paste. In the sintered joint, the Ag sintered layer forms sound metallurgical bonds with both the Cu substrate and the graphite-modified layer. When the sintering temperature is 250 °C, the joint exhibits a shear strength of 30 MPa, which is significantly higher than that of a directly brazed joint. This strategy effectively reduces thermal residual stress in the joint during cooling and shifts the failure location from the brittle graphite substrate to the ductile Ag sintered layer, thereby substantially enhancing the mechanical performance. Full article

This study aims to demonstrate the feasibility of transferring alkali activation technology to the ceramic tile production by developing tiles based on metakaolin and ceramic tile waste by uniaxial pressing. Optimization of the tile formulations was achieved by adjusting precursor composition (metakaolin or combination of metakaolin and ceramic tile waste), NaOH molarity, and overall water content. After uniaxial pressing at 50 MPa, alkali-activated tiles were consolidated at 50 °C for 24 h. Physical and mechanical properties were assessed following ISO test methods for ceramic tiles, allowing direct comparison with the ISO classification requirements. The more promising formulations highlight a water absorption by vacuum test method (ISO 10545-3) equal to 15%, thus allowing a BIII classification according to ISO 13006. Finally, thermal stability up to 850 °C was determined, thus allowing alkali-activated tiles to be industrially glazed. Full article

Electrical measurements of emerging materials such as thin films, two-dimensional materials, and fragile porous systems are often hindered by damage and contamination caused by conventional contact methods, including metal electrode deposition. In this study, we demonstrate the novelty and advantages of a mechanically compliant “soft probe” over conventional methods and conductive AFM. The non-destructive soft probe achieves stable electrical contact in the repulsive-force regime using a hairpin-shaped spring structure, allowing consistent measurements without active force control nor electrode fabrication. Case studies demonstrate that the soft probe prevents metal penetration and preserves intrinsic properties, as demonstrated in NiO resistive switching devices, and improves interface quality compared to deposited electrodes in ferroelectric measurements. It also enables electrical characterization of fragile materials such as metal–organic frameworks without inducing structural degradation. Furthermore, its mechanical compliance ensures stable operation under vibration and thermal stress, enabling measurements in vacuum and low-temperature environments. These results indicate that the soft probe provides a simple, versatile, and contamination-free platform for reliable electrical measurements, and represents a promising approach for the characterization of a wide range of emerging material systems. Full article

This study presents numerical and experimental investigations of a voltage-controlled active preload adjustment system for an ultrasonic traveling wave piezoelectric motor intended for potential use in space-related systems. The proposed preload system consists of two ring-shaped piezoceramic elements driven by a DC voltage of up to 300 V_DC. The passive conical spring provides the nominal rotor preload, while the piezoelectric ring stack enables open-loop remote fine adjustment of the stator–rotor contact force by modifying the axial compression of the spring. Finite element simulations were performed over a temperature range from −25 °C to 55 °C to evaluate the electromechanical response and thermal sensitivity of the preload system. The numerical results indicated that the active preload system can generate a simulated preload force variation of approximately 0.47 N at 300 V_DC, corresponding to approximately 21.4% of the nominal initial preload force of 2.2 N. Experimental tests were conducted in a thermal vacuum chamber at a pressure of 5.6 × 10⁻⁶ mbar. The measured displacement of the piezoceramic preload stack ranged from 0.33 µm to 2.36 µm and showed good agreement with the numerical displacement results. Motor speed measurements demonstrated that increasing the preload-control voltage from 0 to 300 V_DC resulted in an average angular speed increase of approximately 17–20 RPM, depending on temperature. The results demonstrate that the proposed system can provide compact open-loop preload fine adjustment under thermal vacuum conditions, with preload force variation supported by FEM estimation and experimentally validated displacement response. Full article

Slip ring–brush assemblies are widely used in satellite mechanisms to transmit power and signals across rotating interfaces. Under authentic space environments—vacuum, radiation-dominated thermal exchange, and long-duration operation—the coupled effects of mechanical contact dynamics, electrical conduction, intermittent separation, and arcing can accelerate wear and degrade reliability. This paper presents a surface-resolved multiphysics model for multi-track slip rings with staggered brushes. The ring surface is discretized on a circumferential–axial grid and endowed with correlated 3D roughness, enabling interference-based asperity contact. Brush normal dynamics (mass–spring–damper) convert runout and micro-vibration into normal-force ripple and separation events. Electrical conduction is modeled by a parallel admittance network combining pressure-dependent micro-contact conduction and an event-based arc channel activated by separation, opening velocity, and current density with stochastic ignition. A 2D thermal model with ADI integration accounts for Joule/friction heating, radiative cooling, and optional hub conduction. Wear evolves via an Archard-type mechanical term and an arc-energy-driven erosive term. A FAST–MACRO multiscale scheme (20 s FAST, 100 h MACRO with periodic recalibration) enables tractable long-horizon wear prediction while preserving arc statistics. Baseline simulations for a 28 V bus demonstrate rare but nonzero arc activity and predict spatially non-uniform wear at the micrometer scale after 100 h. Full article

The drying kinetics and quality attributes of Polygonatum cyrtonema Hua (PCH), including color, rehydration efficiency, microstructure, and oxidation resistance, were systematically evaluated under various drying methods: hot-air drying (H-D), infrared drying (IR-D), microwave drying (M-D), freeze-drying (F-D), and vacuum drying (V-D). The results indicate that the Midilli model provides the best fit for the experimental data. Among the five drying methods, hot air drying (H-D) is extensively utilized due to its well-established technology; however, its drying performance is relatively average. M-D and IR-D exhibit high drying rates attributed to their strong thermal permeability. Notably, M-D achieves the highest drying rate, with a drying time of only 1/83 that of F-D, yet it demonstrates a relatively low retention rate of total polysaccharides. Furthermore, while IR-D offers fast drying rates, low energy consumption, and favorable color preservation, it performs poorly in preserving the microstructure, active component content, and oxidation resistance of PCH. By contrast, F-D and V-D exhibit significant advantages in maintaining antioxidant activity, active ingredients, and flavor. Nevertheless, F-D requires an extended duration (1080 min), leading to high energy consumption, which restricts its large-scale industrial application. This comprehensive analysis revealed that V-D achieves an optimal balance between energy consumption and product quality, demonstrating substantial advantages and providing a critical reference for the industrial drying production of PCH. Full article

This study provides a rigorous analysis of the phase stability, mechanical behavior, and surface integrity of a non-equiatomic (FeCoNiCr)₈₅Ga₁₅ high-entropy alloy (HEA). By transitioning from the conventional equiatomic design to a gallium-doped 3d-transition metal matrix, we explore the interplay between lattice distortion and phase separation. Synthesized via vacuum arc melting, the as-cast alloy exhibits a non-homogeneous dendritic morphology consisting of a Cr-Fe-Co rich face-centered cubic (FCC) matrix and Ni-Ga rich body-centered cubic (BCC) interdendritic regions. While global thermodynamic criteria (δ = 3.65, ΔH_mix = −9.28 kJ/mol, and Ω = 2.23) favor single-phase solid solution stability, the Valence Electron Concentration (VEC = 7.46) precisely forecasts this dual-phase structure. Following low-temperature annealing at 250 °C for 24 h, high lattice strain energy drives a significant morphological transformation where the continuous interdendritic network resolves into discrete, phase-separated B2/BCC “islands”. Mechanical and tribological characterizations reveal that this low-temperature thermal activation triggers precipitate hardening; the macro-hardness increases from 146 ± 11 HB to 153 ± 7.5 HB and the micro-hardness rises from 186 ± 4 HV_0.5 to 206 ± 17.5 HV_0.5, yielding enhanced resistance to oxidation-delamination wear. However, electrochemical evaluation in a 3.5 wt.% NaCl solution highlights a fundamental trade-off: the formation of localized galvanic micro-cells between the phase-separated islands and the matrix causes the corrosion current density (i_corr) to increase from ≈10⁻⁹ A/cm² in the as-cast state to ≈10⁻⁶ A/cm² post-heat treatment, accompanied by a heightened susceptibility to localized pitting. These findings elucidate the primary role of electronic structure and minor p-block additions in regulating the lifecycle performance of transition metal HEAs under extreme conditions. Full article

The aim of the study was to investigate the effect of enriching carrot slices by NFC (not from concentrate) juices from chokeberry (CH), sea buckthorn (SB), cherry (CHE) and carrot (CA) before microwave-vacuum (MVD) and freeze-drying (FD) carrot on the physicochemical and thermal properties. While water activity (AW) was not dependent on enrichment treatment but only on drying method, NFC juices significantly enriched carrot slices with biocomponents. Freeze-dried samples, as a reference, had significantly lower AW than those dried by the MVD method. Both FD and MVD-dried samples had comparable polyphenol content and DPPH antioxidant activity (AA), but the MVD-dried samples exhibited higher ABTS antioxidant activity. Carrot enrichment in chokeberry and cherry juices resulted in up to six and 10 times higher TPC than in the raw material. In addition, samples enriched in these juices and dried with FD proved to be the most stable in terms of water state and glass transition temperature (61.4 and 69.6 °C) and water activity (approx. 0.10). In FTIR analysis, all samples exhibited similar spectral shapes, indicating similar chemical composition and functional group composition. Only in the spectral region below 900 cm⁻¹ were unique molecular vibrations induced by various organic compounds present. Enriching carrot in juices and MVD can lead to increased hardness (Fmax and breaking work), although this is associated with increased crispness, resulting from the microstructure with a large number of small pores, especially in MVD samples enriched with cherry, chokeberry, and carrot juices, with scores of 8.0–8.4 In this respect, the average crispness rating of the MVD samples (7.2) exceeded that of the FD samples (6.8). If there is a requirement for crunchiness in the future production of dried vegetables as snacks, changes in hardness should be prioritized, along with color and biocomponent content. Full article

Molecular on-surface photochemistry has emerged as a promising alternative to thermal activation for fabricating low-dimensional carbon-based nanomaterials, offering unique advantages such as non-thermal initiation and high chemoselectivity. Controlling the selectivity and efficiency of on-surface photoreactions remains challenging due to the complex interplay among molecular excitation pathways, substrate properties, and reaction conditions. This review briefly summarizes recent advances in light-driven on-surface synthesis under ultra-high-vacuum conditions. We focus on molecular photoexcitation pathways that can be probed by scanning tunneling microscopy and spectroscopy (STM and STS). Studies of light-driven reactions in three categories are overviewed, i.e., dehalogenative C-C coupling, [2+2] and [4+4] cycloadditions, and photoisomerization. Typical strategies for tuning reactivity are exemplified, including molecular pre-organization via self-assembly, surface passivation, and wavelength/polarization control. The summary of successful case studies may not only facilitate the fundamental understanding of on-surface photochemistry but also inspire the design of functional low-dimensional architectures and light-responsive molecular devices. Full article

The catalytic upgrading of vacuum residue (VR) is constrained by the high cost, diffusional limitations, and rapid deactivation of conventional zeolite-based catalysts due to severe coking. Addressing this, we developed novel, low-cost, and coke-resistant catalysts utilizing naturally abundant Iraqi kaolin. A composite support comprising 80 wt.% Iraqi red kaolin and 20 wt.% white kaolin was synthesized via thermal activation at 800 °C and acid leaching. This support was subsequently impregnated with transition and rare-earth metals (Ni, Co, Ce) at 3–40 wt.% loadings, and comprehensively characterized using XRD, BET, SEM-EDX, and XPS. Catalytic performance was evaluated during VR upgrading in a fixed-bed batch reactor at 450 °C. Among the formulations, the 20 wt.% Ce-loaded catalyst (MKRW-800A@Ce20%) exhibited superior efficiency, achieving 80.15% VR conversion, 61.04% liquid yield, and minimal coke formation (3.81 g) compared to Ni and Co counterparts. This enhanced activity is attributed to synergistic effects of improved surface acidity, textural accessibility, and the Ce³⁺/Ce⁴⁺ redox couple, which promotes selective cracking while suppressing coke precursors. These findings provide new insights into the rational design of natural clay-based catalysts, establishing Ce-modified metakaolin as a viable, sustainable alternative to zeolites for industrial heavy-oil processing. Full article

We engineered a compact methanol steam reforming (MSR) system tailored to power a 1 kW High-Temperature Proton Exchange Membrane (HT-PEM) fuel cell. The unit integrates an evaporator, reformer, and burner within a cylindrical titanium-alloy vacuum flask to minimize parasitic heat loss. Guided by an Artificial Intelligence Complex System Response (AICSR) framework, we developed a segmented catalyst architecture that positions an optimized Pd/ZnO/Al₂O₃ catalyst downstream of a commercial Cu–Zn catalyst bed. This spatial configuration reduces palladium consumption by >50% while maintaining a hydrogen generation rate of 8000 sccm at 250 °C. During a 40 h stability test, the system exhibited a low deactivation rate of 0.235% h⁻¹, with methanol conversion decaying gradually from 98.1% to 88.7%. The downstream PdZn intermetallic phase actively promoted the water–gas shift (WGS) reaction, restricting CO concentration to an average of 3.9% (minimum 2.5%). Achieving a system thermal efficiency of 88.589% and a 20 min startup time, this design validates AI-assisted spatial catalyst distribution as a highly viable strategy for compact hydrogen generation. Full article

This study presents a comparative evaluation of four drying methods for carrot, red beet, and pumpkin pomace to produce natural functional food ingredients. The work addresses the valorization of 35–45% vegetable processing waste—a rich source of bioactive compounds—aligning with circular bioeconomy principles and Kazakhstan’s goals for deep processing of agricultural raw materials. The compared methods were convective drying (CD), ultrasound pretreatment + convective drying (US + CD), vacuum-microwave drying (VMD), and ultrasound pretreatment + vacuum-microwave drying (US + VMD). Drying kinetics, water activity, physicochemical and functional properties of powders, retention of bioactive compounds, color characteristics, thermal stability, and sensory attributes were assessed. Kinetics were fitted using Midilli et al., Page, and Weibull models. US + VMD provided the highest drying acceleration (6–11 times faster than CD), reaching final moisture of 5.1–5.9%, water activity a_w 0.27–0.31 in 80–170 min, and bioactive compound retention of 90–95% (carotenoids 92–95%, betalains 90–94%). It also delivered superior flowability (Carr’s index 22.5–30.4%), dispersibility (80–88% in 30 s), and thermal stability (75–85% at 200 °C). Acceleration varied by raw material: maximum for beet (up to 11×) due to soluble sugars and nitrates, minimum for pumpkin (5.5–8×) due to dietary fibers and pectins, and intermediate for carrot (6–9×) influenced by carotenoids’ dielectric properties. The results highlight US + VMD’s strong potential for producing functional powders to replace synthetic additives in food systems. Effective method selection and parameter optimization require consideration of raw material type and rheological characteristics. Full article

In this study, Ti-Co-Ce getter films were deposited via magnetron sputtering to investigate their activation mechanism—the thermal removal of surface passivation layers to restore gas sorption capability. The morphology before and after film activation was characterized using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The oxygen content on the film surface before and after activation was measured using an energy-dispersive X-ray spectrometer (EDS), and gas desorption during activation was monitored with a quadrupole mass spectrometer (QMS). The combined results confirmed the absence of O₂ desorption during activation, suggesting oxygen migration into the film bulk. Crucially, in situ X-ray photoelectron spectroscopy (XPS) combined with controlled Ar⁺ ion sputtering depth profiling (0–30 nm) was employed to directly probe the chemical-state evolution within the thin film before and after thermal activation at 400 °C, thereby providing direct evidence of the activation dynamics. The data reveal that within the 0–10 nm near-surface region, a strong oxygen chemical potential gradient drives rapid oxide reduction and inward migration of lattice oxygen. At depths of 20–30 nm, moderate reduction coupled with oxygen enrichment induces phase separation, while around 30 nm, a dynamic equilibrium between oxygen inflow and outflow is established. These findings provide a theoretical basis for optimizing activation processes and guiding the development of low-temperature getter materials. This work is particularly relevant for MEMS, vacuum electronics, and other applications with stringent thermal budgets, expanding the design possibilities for heat-sensitive device integration. Full article

Tamarillo (Solanum betaceum) processing is characterized by early biomass exclusion and thermal stabilization, which may limit in-process retention of phytochemicals. This study evaluated an integrated sequence combining Flash Vacuum Expansion (FVE) under different processing conditions with whey protein-based cryostructuring as a strategy to enhance the redistribution and structural immobilization of tamarillo bioactives. FVE promoted migration of phenolics and pigments prior to mechanical fractionation. Selected FVE-treated puree was incorporated into a whey protein matrix and subjected to cryostructuring and freeze-drying to generate a porous stabilization scaffold. Structural characterization by scanning electron microscopy and gas adsorption confirmed the formation of an interconnected porous matrix. Cryostructuring reduced water activity to 0.17 ± 0.01 and produced high porosity (91.9%) with low bulk density (0.109 g·cm⁻³). Total phenolic retention exceeded 83%, while anthocyanins showed greater sensitivity (46% retention). No statistically significant additional losses of phenolics or antioxidant activity were observed during cryostructuring relative to gelation. The integrated approach illustrates a process-level stabilization pathway in which redistributed phytochemicals are physically confined within a porous scaffold, providing a structurally differentiated alternative to conventional drying for improved in-stream resource utilization. Full article