Search Results (2,264)

This paper investigates an Organic Rankine Cycle (ORC) system for low-to-medium temperature heat recovery using comparative thermodynamic, exergoeconomic and economic modelling. A working-fluid study considering environmental and thermodynamic perspectives is conducted. A 20 kW ORC unit is tested and used as a feasibility and trend-consistency reference to support the modelling assumptions and practical operating bounds. A parametric study then examines the effects of evaporator pressure, condensation temperature, superheat, subcooling and heat-exchanger pinch-point temperature differences on net power output, first- and second-law efficiencies, total product cost and total capital investment under prescribed boundary conditions. Multi-objective optimization is applied to identify Pareto-optimal trade-offs and representative compromise solutions. Results show an intermediate evaporator pressure maximizes net power output, while lower condensation temperature generally improves efficiency; superheat has limited efficiency impact but should ensure safe operation, and a small subcooling margin (around 3 °C) mitigates cavitation risk. The best overall performance is obtained with an evaporator pinch of 3 °C and a condenser pinch of 5–9 °C; tightening pinch constraints increases required heat-transfer area and makes heat exchangers the main cost bottleneck for high-efficiency solutions. Full article

The goal of this research is to minimize the electrical energy consumption and emissions of the refrigeration cycle as a step towards sustainable refrigeration. The Vapor Compression Cycle (VCC) relies mainly on electrical energy; however, the developed Heated Vapor Compression Cycle (HVCC) relies on electrical energy as well as solar energy, which lowers our dependence on electrical energy and improves environmental sustainability. The objective of this research is to improve the coefficient of performance (COP) of the HVCC in comparison to the VCC by adding an intermediate flash tank to the capillary tube. The intermediate flash tank converts the wet refrigerant into saturated liquid, which decreases the quality of the refrigerant at the entrance of the evaporator and consequently improves the cooling potential, i.e., the cooling power. The proposed concept was examined for four different refrigerants, i.e., R502, R407c, R22 and R410a, and at four different intermediate pressures. Also, the influence of the heating temperature on the HVCC as a function of intermediate pressure was examined. It was found that, for all the examined refrigerants, decreasing the intermediate flash tank pressure improves the COP of the cycle. The HVCC operating with R410a has the highest COP, i.e., 6.2, at an intermediate flash tank pressure of 165 psi and a heating temperature of 100 °C, while R407c has the highest COP of 4.8 when compared with R502 and R22 when operating under the same pressures. Adding a flash tank to the HVCC operating with refrigerant R410a can improve the COP of the cycle by more than 40% and by more than 25% in the case of refrigerant R407c. Such improvement in the performance of the cycle reduces electrical energy consumption and improves the environmental sustainability of the cycle. Full article

High-temperature Daqu (HTD)’s quality determines the characteristics and yield of the Chinese sauce-aroma baijiu. However, winter production frequently encounters challenges such as fermentation instability and metabolic fluctuations, primarily stemming from complex, unmonitored microenvironmental changes within the HTD pile. This study established a closed-loop system linking the microenvironment, HTD quality, microbiome, and metabolome. Through continuous monitoring of the winter fermentation pile’s microenvironmental conditions and integrating multi-omics analyses, we revealed that CO₂ concentration within fermentation piles is the core factor causing quality variations in HTD. By breaking the respiratory bottleneck formed by carbon dioxide (CO₂) accumulation through the turning anaerobic stress can be alleviated, thereby driving metabolic succession. The study found that vertical CO₂ concentration heterogeneity severely restricts the enrichment of aerobic core functional microbial communities such as the Bacillus species. This directly blocks key metabolic pathways including amino acid metabolism and energy supply via ABC transporters. Moreover, the specific accumulation of Amadori products further confirms that this low-temperature environment under CO₂ stress causes the Maillard reaction to stall at intermediate stages. Consequently, this study proposes a steady-state control strategy centered on oxygen and CO₂ gas characteristics. By actively regulating the gaseous microenvironment to eliminate metabolic heterogeneity, it provides theoretical support for standardizing traditional fermentation processes. Full article

Electrical Discharge Machining (EDM) enables precision post-weld finishing of AISI 304 stainless steel, but stochastic spark overlaps make the fatigue-critical maximum peak-to-valley height (R_max) difficult to predict. This study develops a validated physics-based framework quantifying how crater overlap governs R_max evolution. Experiments on unwelded AISI 304 cylinders—proxying weld metal while excluding heat-affected zone (HAZ) effects—used Central Composite Design (20 trials, 900–9380 μJ discharge energies). Profilometry and scanning electron microscopy (SEM) correlated the crater size, overlap intensity, micro-cracking, and R_max escalation from 18 to 85 μm. Primary and secondary crater formation under minimum and maximum overlap configurations were simulated using a 2D axisymmetric finite element model with Gaussian heat flux and temperature-dependent thermophysical properties. The predictive metric R_max,num = (d_initial + d_secondary)/2 achieved 11–19% average error against the experimental R_max,exp, with complementary valley depth (R_v) validation at 13% error. The Specimen 7 outlier (~50% error) reveals the limitations of deterministic modelling under stochastic debris accumulation and plasma instability at intermediate energies. Crater overlap generates secondary dimples, sharp inter-crater peaks, and rim micro-crack networks, driving the 4.7-fold R_max increase—approaching International Institute of Welding (IIW) fatigue thresholds (<25 μm for high-cycle categories). The framework explicitly links the discharge energy, plasma channel radius (R_pc), and overlap geometry to surface topography, enabling process optimization (I·t_on < 60 A·s maintains R_max < 25 μm). Mesh independence (<2.5% convergence) and six centre-point replicates (CV = 4.2%) confirm robustness. This validated upper-bound R_max predictor supports the digital co-optimization of welding and EDM parameters for aerospace/energy applications, with planned extensions to stochastic 3D models incorporating adaptive remeshing and real weld topographies. Full article

To investigate the heat-generation mechanisms of journal bearings under different whirl motion and to clarify the corresponding temperature distribution characteristics, a computational fluid dynamics-based method was developed. The model incorporates temperature-dependent lubricant viscosity and employs an unsteady dynamic-mesh updating approach based on structured grids, enabling the automatic iterative tracking of the journal center during whirl motion. A thermal-effect analysis model that accounts for journal whirl trajectories was thereby established. The whirl orbit shape is characterized using elliptical eccentricity, and the effects of whirl direction, elliptical eccentricity, and whirl frequency on the circumferential temperature and pressure distributions of the journal are examined. Results show that under forward whirl, increasing whirl frequency and elliptical eccentricity initially enhances and then weakens local hydrodynamic pressure and viscous shear dissipation in the oil-film convergent region, producing pronounced first-order circumferential temperature nonuniformity and a high risk of thermal bending at intermediate frequencies. Under backward whirl, hydrodynamic effects are reduced and heat generation shifts from localized concentration to global shear dissipation, forming a relatively uniform second-order circumferential temperature field. Increasing elliptical eccentricity causes the whirl orbit to become more linear, improving load-carrying capacity and heat-transfer performance and thereby mitigating thermally induced vibration and oil-film whirl instability. Full article

Climate change influences the agronomic behaviour of fruit trees. It is necessary to determine which cultivars adapt best to conditions in which water supplies are becoming increasingly scarce. This study analyses different phenological, morphological, physiological, agronomic and productive parameters to evaluate water stress tolerance in six late-blooming almond cultivars widely grown in Spain (‘Ferragnès’, ’Francolí’, ‘Masbovera’, ‘Glorieta’, ’Guara’ and ‘Lauranne’). Two different plots were analysed: one under regulated deficit irrigation, at Les Borges Blanques, Lleida, with a water deficit (146.2 mm/year) and the other under rainfed conditions, at Mas Bové, Constantí, Tarragona, with a water deficit (284.5 mm/year). Parameters, including an increase in canopy volume, leaf-to-air thermal gradient, and slope between leaf water potential and level of leaf saturation, have proven to be good indicators of resistance to water stress. Yield variation and leaf temperature variation between rainfed and irrigated conditions also perform quite well. An assessment of leaf chlorophyll content, measured using SPAD-502, suggested the presence of a collateral effect resulting from the opacity of the biomass, as well as to chlorophyll-related cuticular colouring. Finally, under the experimental conditions, ‘Guara’ and ‘Masbovera’ proved the most resistant cultivars; ‘Glorieta’ and ‘Francolí’ exhibited an intermediate level, and ‘Lauranne’ and ‘Ferragnès’ were the least resistant cultivars. Full article

We have investigated the major- and trace-element composition of hydrothermal pyrite, magnetite, and Ti-magnetite, and of the principal Cu-minerals chalcopyrite and chalcocite, to constrain ore-forming processes in the northeastern Saveh district (central Urumieh–Dokhtar magmatic arc, Iran). Our data provide new constraints on the magmatic–hydrothermal evolution and subsequent hydrothermal–supergene modification of the ore system. Ti-magnetites hosted in monzodioritic intrusions are enriched in Ti–V–Al, plot below the magnetite–ulvöspinel join and record high crystallization temperatures (<500 °C) under relatively low oxygen fugacity. By contrast, magnetite from silica-rich hydrothermal veins is Fe-rich with very low TiO₂; it formed at intermediate temperatures (~200–300 °C) under higher fO₂ and is markedly depleted in Ti and V compared with the intrusive oxides. Textures and oxide systematics (Al + Mn vs. Ti + V; V/Ti–Fe) document repeated hydrothermal pulses, Fe²⁺ leaching and element redistribution during cooling and fluid–rock interaction. Geochemical trends indicate progressive evolution from a magmatic fluid to later meteoric water overprint, with increasing As contents reflecting cooling and mixing with meteoric waters. Vertical elemental zoning suggests that most samples represent mid- to deep-level sections of the epithermal system. Elevated Cu contents (up to 0.95 wt.%) highlight pyrite as a significant Cu host. Co/Ni ratios between 1 and 10 further corroborate a magmatic–hydrothermal origin. Chalcopyrite is the principal economic Cu carrier at Northeast Saveh. Replacement follows a temperature- and fluid-controlled pathway (chalcopyrite → covellite → chalcocite). At lower temperatures (<~200 °C) replacement proceeds more slowly, producing chalcocite/digenite under prolonged reaction conditions. Chalcocite commonly occurs as thin replacement rims and fracture fills that concentrate remobilized copper. Collectively, the investigated oxide and sulfide proxies provide robust discriminants for separating magmatic versus hydrothermal domains and for vectoring toward higher-temperature feeders and zones of remobilized copper. Full article

As large language models (LLMs) are increasingly used as digital respondents and generative agents in computational social science, prior work has primarily focused on the fidelity of their expressed opinions, often overlooking a fundamental question: the behavioral stability of outputs across repeated runs of the same model when the persona specification and task conditions remain unchanged. This paper proposes a behavioral stability evaluation framework for role-playing tasks, using the Political Compass questionnaire as the testbed. The questionnaire maps responses onto a two-dimensional coordinate system defined by an economic axis and a social axis, enabling political orientations to be directly quantified and compared in a continuous space. To ground the simulation in realistic user behaviors, we construct personas from publicly available social media texts and stratify them based on Political Signal Clarity. Across three LLMs, we compare repeated questionnaire completions under different decoding temperatures and prompting strategies. We characterize it along two complementary dimensions: dispersion of the resulting two-dimensional coordinates across runs, measured by an Overall Stability Score (OSS), and dispersion of per-item choices across runs, quantified by response entropy. We further use linear mixed-effects models to account for persona-level heterogeneity and to estimate the effects of key factors on stability. Our results show that coordinate drift and item-level dispersion do not always move in tandem. Increasing temperature typically amplifies variability, although models differ in their sensitivity. Contrary to its success in reasoning tasks, Chain-of-Thought (CoT) prompting failed to enhance stability in this value-laden context. Instead, it frequently amplified coordinate drift by introducing stochasticity into intermediate reasoning steps. Results show that LLMs exhibit greater behavioral stability when role-playing personas with clearer political signals. These findings suggest that stability should be treated as a pre-study benchmark before deploying LLM-based role-playing simulations, and that key generation settings and stability statistics should be reported alongside substantive conclusions. Full article

To realize the efficient recovery and utilization of rare earth resources, this study systematically investigates the preparation process of recycled-rare earth polishing powder using rare earth intermediates (purified from waste polishing slag) as raw materials. This work focuses on two core stages: precursor synthesis and high-temperature calcination. During the precursor preparation stage, the particle size of the precursor was controlled by optimizing the ball milling process (with a ball milling time of 1 h, a ball-to-material ratio of 3:1, and 2 mm zirconia balls), yielding an optimal D50 of 6.5 μm. The Ce/La ratio was modulated by adding cerium carbonate (the conventional ratio is 65:35, which can be adjusted as needed within the range of 65:35–80:20). Furthermore, fluorine (3–7%) and a small amount of praseodymium were incorporated to enhance the polishing performance. In the high-temperature roasting stage, single-factor tests were conducted to determine the optimal staged heating rates (below 400 °C: 5 °C/min; 400–700 °C: 3 °C/min; above 700 °C: 1.5 °C/min) and a holding time of 4 h at 950 °C. Under these optimized conditions, the resulting polishing powder exhibits a material removal rate exceeding 350 mg·h⁻¹ and maintains stable performance over three consecutive polishing cycles. This study demonstrates that by regulating the chemical composition and physical parameters of the precursor, as well as optimizing the high-temperature roasting process, recycled-rare earth polishing powders with tailored performance characteristics can be custom-manufactured. This approach balances the polishing ability and production cost, thus providing technical support for the industrial production of recycled-rare earth polishing powder. Full article

Waste oyster shell powder (OP) and calcined oyster shell powder (COP) were used as bio-fillers in asphalt mastics. Limestone powder (LP) served as the control. This study employed rheological theory to quantify filler–asphalt interactions. Dynamic shear rheometry (DSR), Black diagrams, and master curves were analyzed to determine critical volume fraction (φ_crit), interaction parameter (C), and complex viscosity increment (∆η*). Results indicate that OP mastics exhibit the lowest φ_crit (0.510) and highest C value (1.133), demonstrating the strongest interfacial interaction. COP shows intermediate interaction strength (φ_crit = 0.542), yet both OP and COP outperform LP (φ_crit = 0.617) in high-temperature deformation resistance within the 0.23–0.53 filler volume fraction range, evidenced by superior complex shear modulus (G*) master curves and pronounced ∆η* increases. Grey relational analysis identifies specific surface area and CaCO₃ content as governing factors. Optical microscopy and FTIR confirm that filler–asphalt interactions are dominated by physical adsorption without chemical bond formation. These findings elucidate the performance advantages of both raw and calcined oyster shell powders and provide a theoretical basis for their application as sustainable high-performance bio-fillers in asphalt pavements. Full article

Test specimens fabricated from 42CrMo4 steel were subjected to heat treatment comprising quenching followed by high-temperature tempering. This treatment is commonly referred to as hardening, and the result is a tempered sorbite microstructure that provides a balanced combination of strength and plasticity. In order to improve the hardness and wear resistance of the contact surfaces, two types of physical vapor deposition (PVD) coatings were deposited onto the specimens: the first was a two-component architecture Cr/CrTiAl and the second was a multilayer Cr/(CrTiAl)N/CrTiAl. In both configurations, an intermediate chromium adhesion layer was initially deposited to enhance interfacial bonding with the substrate. The adhesion strength of the deposited coatings to the steel substrates was evaluated using a standardized adhesion test. The adhesion quality was classified as HF1 (the highest adhesion class in the HF1–HF6 scale, defined in EN ISO 26443), indicating excellent interfacial bonding. The hardness and modulus of elasticity of both coatings were determined through nanoindentation. According to the measured hardness values of the two coatings, 27.3 GPa (Cr/CrTiAl) and 37.5 GPa (Cr/(CrTiAl)N/CrTiAl), they can be classified as hard coatings (hardness greater than 20 GPa). Despite the difference in hardness, the two coatings have comparable elastic modulus values: Eit = 353 GPa for the two-component architecture coating and Eit = 349 GPa for the three-component architecture coating. Tribological characterization was performed using the ball-on-disc method under dry sliding conditions over a total sliding distance of 59 m, whereby the friction coefficient (µ) was recorded. Additionally, the wear rate of the applied coatings was calculated from the measured wear volumes or profiles. The two coatings have comparable friction coefficient values (Cr/CrTiAl–μ = 0.362, Cr/(CrTiAl)N/CrTiAl–μ = 0.325), but the three-component architecture coating Cr/(CrTiAl)N/CrTiAl has a lower wear rate (k = 1.64 × 10⁻⁴) compared to the two-component architecture coating Cr/CrTiAl, which has a wear rate of k = 7.6 × 10⁻⁴. The investigated coatings have hardness, modulus of elasticity and friction coefficient values competitive with those of nitride coatings (two-component architecture and three-component architecture), and their wear rate also corresponds to generally accepted values. Full article

We used synchrotron X-ray diffraction (XRD) and ac-impedance spectroscopy (AIS) to uncover the structural and chemical modifications undergone by RbH₂PO₄ (RDP) at intermediate temperatures (150 °C < T < 300 °C) and investigate their relationship with RDP’s proton conductivity, σ. Nyquist plots collected on RDP samples sealed in a small volume (~50 mL) of dry air show a gradual increase in σ upon heating from 180 to 260 °C, but not the three-order-of-magnitude superprotonic jump observed in the Cs-based compound CsH₂PO₄ (CDP) within the same temperature range. Correspondingly, XRD measurements using synchrotron radiation (λ = 0.922 Å) on RDP crystalline powders sealed in a quartz capillary exhibit no evidence of a monoclinic-to-cubic superprotonic phase transition like the one observed in CDP. Instead, these temperature-resolved powder XRD patterns demonstrate that the intermediate-temperature RDP monoclinic phase (P2₁/m, a = 7.733 Å, b = 6.189 Å, c = 4.793 Å, and β = 109.21 deg) persists up to the melting point of the title compound. Our most significant finding comes from heating RDP under high pressure (P = 1 GPa), which leads to markedly different structural behavior. Indeed, our full profile refinements against XRD data collected on RDP crystals compressed at ~1 GPa show evidence of a polymorphic phase transition (at T_c = 300 °C) to a high-temperature cubic phase (Pm-3m, a = 4.784 Å) that is isomorphic with its CDP counterpart. This is significant, as it indicates that the superprotonic conduction in phosphate solid acids is not cation-specific, and a general highly efficient proton conduction mechanism is present in the high-temperature phases of these materials. Full article

As a critical climate regulator on the Qinghai–Xizang Plateau, Qinghai Lake exerts important influences on surrounding surface environmental conditions. Using MODIS remote sensing data and topographic information from 2000 to 2024, this study analyzed the spatiotemporal variations in land surface temperature (LST), normalized difference vegetation index (NDVI), and temperature vegetation dryness index (TVDI) in the 10-km riparian zone. The buffer was subdivided into five 2-km distance gradients to quantify the attenuation of lake effects and their interaction with topographic factors. The results indicate pronounced seasonal contrasts and distance-dependent differentiation of surface variables. LST exhibited clear seasonal variability, with peak values in the second and third quarters (Q2 and Q3). During Q2, the near-shore zone (0–2 km) remained notably cooler by approximately 2–3 °C (23.8 °C) than intermediate and distal zones (25.4–26.8 °C), indicating a moderate lake-related cooling effect during the early warm season. NDVI showed consistent seasonal phenology across all buffers, reaching maximum values in Q3, while mean NDVI values increased gradually with distance from the lake, ranging approximately from 0.48 in the near-shore zone to 0.51 in the distal zone. TVDI displayed distinct seasonal and spatial patterns, with relatively low and stable values in the near-shore zone throughout the year and a pronounced seasonal minimum in the distal zone during Q3 (0.57). These findings highlight strong seasonal and spatial heterogeneity of surface environmental conditions in the Qinghai Lake riparian zone. The observed patterns suggest that lake proximity and topographic gradients jointly influence hydrothermal conditions and vegetation dynamics at the landscape scale, providing quantitative evidence for understanding surface–environmental gradients in alpine lake systems. Full article

The Seulawah Agam volcano, located in Aceh, hosts one of Indonesia’s largest unexploited geothermal resources that is included in the Indonesian Green Energy Program. Previous studies of the Seulawah geothermal system (SGS) have used partial data and methods without developing a comprehensive conceptual model of the reservoir and its fluid flow and heat transfer patterns. This study aims to characterize the groundwater flow and heat transfer patterns of the SGS through numerical modeling based on integrated geological, geophysical, and geochemical data. Numerical modeling was conducted along two representative transects: Ie Seum, Ie Jue, and Kawah van Heutsz manifestations. MODFLOW 6 was used to model groundwater flow and heat transfer using a new conceptual model derived from magnetotelluric data, chemical composition and physical properties of the fluid, isotopic data, and mineragraphic data. The low resistivity anomalies are closely related to fluid discharges beneath the Ie Seum and Ie Jue areas. The depth of the Ie Seum reservoir is around 1.0–2.5 km, with estimated temperatures of 120–242 °C, while the depth of the Ie Jue and Kawah van Heutsz reservoirs is between 0.8 and 2.5 km, with estimated temperatures of 150–316 °C. The modeling suggests that the Ie Seum and the Ie Jue–Kawah van Heutsz systems represent regional groundwater and intermediate-local flow regimes, respectively. It is suggested that drilling be conducted around the local Ie Jue hydrothermal system, which is more economical given the shallower reservoir and higher temperature. Full article

Direct conversion of CO₂ into fuels or chemicals using solar energy has long been a topic of interest among researchers. However, the severe recombination of photogenerated carriers in photocatalysts often results in low conversion efficiency. To synergistically utilize both the light and thermal energy components of sunlight, this study designed a structurally simple Zn-Co bimetallic catalyst to enhance photocatalytic efficiency while lowering the temperature required for the thermal catalytic reaction. Through screening different precipitants, it was found that the Zn-Co catalyst prepared with NH₃ as the precipitant exhibits outstanding activity for CO₂ hydrogenation to methane at 240 °C, with CH₄ selectivity exceeding 93%. Under the same conditions, the photothermal synergistic effect leads to an approximately 10% increase in turnover frequency (TOF). Structural characterization revealed that the NH₃ precipitant effectively modulates the crystal phase, surface active sites, and electron transfer efficiency of the catalyst, thereby influencing the formation and desorption rates of key intermediates such as CO*, HCOO*, and *OCH₃ during CO₂ hydrogenation. The optimal photothermal synergy observed in this system further highlights the potential of catalyst design for achieving targeted product control. Full article