Search Results (1,244)

Rapid urban expansion and agricultural development have substantially altered land use/land cover (LULC), surface thermal regimes, and ecosystem conditions in semi-arid cities. This study investigates the spatiotemporal dynamics of LULC and evaluates their associations with land surface temperature (LST), vegetation health, soil moisture, and drought conditions in Ghazni City, Afghanistan, between 2013 and 2023 using a Google Earth Engine (GEE)-based framework. Landsat 8 OLI/TIRS imagery was classified using a Random Forest (RF) algorithm, while the Normalized Difference Vegetation Index (NDVI), Soil Adjusted Vegetation Index (SAVI), Vegetation Condition Index (VCI), Temperature Condition Index (TCI), Vegetation Health Index (VHI), and LST were derived to evaluate environmental responses. To provide a comprehensive evaluation of urban–climate interactions, monthly Landsat-derived LST time series were analyzed and compared to MODIS and ERA5 datasets through a multi-source consistency assessment framework. The RF classification achieved overall accuracies of 95.56% (2013) and 97.77% (2023), with Kappa coefficients of 0.89 and 0.94, respectively. Results revealed a substantial expansion of built-up areas (5.4%) and vegetation/agricultural land (7.2%), accompanied by a decline in bare land. Urban and barren surfaces consistently exhibited higher LST values, whereas vegetated areas demonstrated a pronounced cooling effect. NDVI and SAVI analyses indicated improving vegetation conditions and soil moisture status over the study period. LST exhibited strong seasonal variability, with summer maxima reaching 49.74 °C and winter minima declining to −8.39 °C. Comparisons among the Landsat, MODIS, and ERA5 datasets demonstrated strong agreement, with a high correlation between Landsat- and MODIS-derived LST (R = 0.84), supporting the reliability of the Landsat-derived LST estimates. Generally, the findings demonstrate the critical role of vegetation in moderating surface temperatures and enhancing urban climate resilience, providing scientific evidence for sustainable land use planning and climate adaptation strategies in semi-arid cities. Full article

Deployable reflector antennas demand high geometric precision; the Ruze equation directly links surface error to RF gain. Arc-shaped CFRP ribs are vulnerable to thermal deformation, as their curvature converts in-plane expansion into out-of-plane displacement, which symmetric laminates cannot suppress. Classical laminate theory (CLT) underestimates the coefficient of thermal expansion (CTE) of cross-ply laminates by factors of 1.75–2.38 for the laminate configurations investigated in this study, causing up to 79.4% of displacement prediction errors in symmetric designs. Here, we present an asymmetric laminate that overcomes both limitations. The upper skin (nine plies) and lower/web skins (seven plies) from the same prepreg batch create a CTE mismatch (Δα = 6.30 × 10⁻⁷ K⁻¹), activating coupling stiffness to generate a thermal moment opposing curvature-driven displacement. Because both skins share identical batch history, CTE prediction errors cancel through common-mode rejection. Compared with the symmetric design, the asymmetric design achieved a 50.4% reduction in thermal deformation (from 210 µm to 104 µm) and improved FEA accuracy from 79.4% error to 4.8% error under experimental schemes. The method uses only conventional 0/90° prepreg and standard autoclave processing, with the upper-surface ply count as the sole design variable for a given section’s geometry, establishing retained coupling stiffness as a practical route to dimensional stability in curved space structures. Full article

Silicone gel (SG) is widely used as a soft encapsulation material for high-voltage power devices because of its excellent flexibility, thermal stability, and electrical insulation. However, its intrinsically low thermal conductivity and susceptibility to partial discharge (PD) at triple-junction interfaces restrict long-term operational reliability. In this study, polydopamine-modified hexagonal boron nitride (P-BN) was introduced into silicone gel to construct thermally conductive and electrically insulating composites. The SG/P-BN composites exhibited reduced filler agglomeration and a more continuous filler–matrix morphology than the corresponding SG/BN composites, while the model-extrapolated trap analysis suggested composition-dependent changes in the higher energy charge trapping states of the P-BN-containing composites. As a result, the SG/P-BN composites exhibited enhanced thermal stability, reduced coefficient of thermal expansion, and improved heat-transfer capability, with thermal conductivity increasing from 0.183 W/m·K for pristine SG to 0.25 W/m·K. The composite containing 2 wt% P-BN showed the best insulation performance, with breakdown strength increasing from 24.05 to 28.45 kV/mm at 25 °C and from 19.59 to 24.71 kV/mm at 150 °C. Under a simplified triple-junction laboratory configuration, the PD inception voltage increased from approximately 3.1 kV for pristine SG to 4.1 kV for SG/P-BN₂, accompanied by fewer high-amplitude discharges. This work demonstrates improved material-level thermal conductivity and electrical insulation performance of P-BN-containing silicone gel composites under the investigated laboratory conditions. Full article

To achieve high interconnect density in 2.5D packages, various microscale structures such as through-silicon vias (TSVs), microbumps, and redistribution layers (RDLs) are employed. These features typically exist at the micron scale, whereas other package components span millimeter to centimeter scales, resulting in a wide range of physical dimensions within the package. Although finite element analysis (FEA) has proven effective for evaluating the mechanical and thermal characteristics of 2.5D packages, the inherent multi-scale nature poses significant computational challenges and numerical convergence issues, severely hindering the design and analysis of increasingly dense packages. To address this problem, this paper proposes an efficient numerical homogenization method for the mechanical and thermal analysis of 2.5D packages. The method employs periodic boundary conditions (PBCs) based on the concept of referential statistical volume elements (rSVEs). In this approach, typical microstructures—including TSVs, microbumps, and RDL traces together with the surrounding matrix material—are treated as a homogeneous medium, and the equivalent material properties of the multi-scale structures are evaluated. These properties include the stiffness matrices (from which the equivalent Young’s modulus, shear modulus, and Poisson’s ratio can be derived), coefficients of thermal expansion, and thermal conductivity. Validation results demonstrate that the proposed method ensures continuity of displacement, stress, strain, and heat flux across opposite surface pairs of the rSVEs. Compared with experimental measurements and other existing homogenization techniques, the method accurately determines the equivalent material properties of complex multi-scale structures without being restricted to specific geometries, while significantly improving computational efficiency. Finally, the proposed numerical homogenization method is successfully applied to wafer warpage analysis during the manufacturing process and to thermal analysis under operating conditions. The results indicate that the method achieves high computational efficiency while maintaining accuracy in both mechanical and thermal analyses of 2.5D packages, thereby laying a solid foundation for the development of next-generation 2.5D package structures. Full article

We review some recent findings on thermal properties of the magnetic dual chiral density wave (MDCDW) condensate in the Nambu–Jona-Lasinio (NJL) model of dense quark matter, as well as a convenient method for investigating this phase with a high-order Ginzburg–Landau (GL) expansion. We show how a recently discovered formula for the GL coefficients can be used to compute key physical properties of the condensate, such as its ground state order parameters and critical temperature in the mean-field approximation and its stability against thermal phonon fluctuations. We find that magnetic fields of order ${10}^{18}$ G significantly increase the condensate magnitude and critical temperature, eventually making the condensate favored up to temperatures a few times 10 MeV over the entire range of densities in the model. At much smaller fields, the condensate is still preferred and thermally stable over a range of densities relevant to cold neutron stars. We emphasize how the topological features of MDCDW are encoded in certain terms of the GL expansion, which can be used to show that the preceding effects have a topological origin. Finally, we present a new result on the convergence properties of the GL expansion, proving that it converges when $|m|+|b|<\sqrt{{\mu }^2+{\left(\pi T\right)}^2},$ where m and b are order parameters proportional to the condensate magnitude and spatial modulation, respectively. This condition holds over a large region of parameter space, including the region of interest for neutron star applications. Full article

Solar energy has become one of the most important renewable energy sources for reducing dependence on conventional fossil-based energy systems. Rooftop photovoltaic (PV) installations play a key role in the expansion of solar energy, particularly in tropical countries such as Vietnam. This study experimentally investigates the effects of roof material, rear ventilation gap, PV technology, solar irradiance, and wind speed on the power conversion efficiency (PCE) of rooftop PV modules under tropical climatic conditions in Ho Chi Minh City, Vietnam. Three roof types (concrete, tiled, and corrugated metal), three rear ventilation gaps (10, 30, and 50 cm), and two PV technologies (monocrystalline and polycrystalline) were evaluated under real operating conditions. The results indicate that increased module temperature significantly reduces power output and PCE, even under high solar irradiance. PV modules installed on corrugated metal roofs exhibited the highest operating temperatures and the lowest efficiencies, whereas concrete and tiled roofs provided more favorable thermal conditions. Increasing the rear ventilation gap enhanced convective cooling, with the 30–50 cm configurations showing superior heat dissipation compared with the 10 cm configuration, particularly for corrugated metal roofs. The experimentally determined heat transfer coefficient ranged from 23.48 to 67.64 W m⁻² K⁻¹, exceeding the theoretical wind-based coefficient (16.86–17.22 W m⁻² K⁻¹), thereby indicating the contribution of mixed convection, radiative exchange, and roof–module thermal interactions. Monocrystalline modules consistently achieved slightly higher efficiencies than polycrystalline modules. The findings provide practical guidance for optimizing rooftop PV installations and improving energy yield in tropical climates. Full article

First-principles calculations were performed to predict the temperature-dependent elastic properties of fcc-disordered Pt–Rh alloys over a range of compositions. Special quasirandom structures (SQSs) were employed to represent the atomic disorder in the fcc solid-solution phase. The vibrational contribution to the free energy was evaluated using the phonon quasi-harmonic approximation, enabling the calculation of finite-temperature free energies and coefficients of thermal expansion for the fcc-disordered Pt–Rh alloys. The elastic stiffness constants at different compositions were determined using the energy–strain method. By combining the calculated thermal expansion coefficients with elastic stiffness data obtained at various volumes, the temperature-dependent elastic stiffness constants of the fcc-disordered Pt–Rh alloys were determined. Full article

Autonomous driving sensor fusion housings (SFHs) integrate LiDAR, radar, camera, and computing modules within a shared mechanical and thermal enclosure. This review examines how coefficient of thermal expansion (CTE) mismatch among housing polymers, aluminum heat spreaders, substrates, and solder joints can contribute to interfacial delamination, solder joint fatigue, optical misalignment, and Thermomechanical Coupling Interference (TMCI). Using a structured narrative review of 99 publications and authoritative standards from primarily 2009 to 2026, the article organizes the evidence into a 4 × 4 taxonomy linking four failure mechanisms with experimental, computational, AI/ML, and qualification-oriented approaches. The review explicitly distinguishes direct literature evidence, transferred package-level evidence, model-based extrapolation, and author-derived conceptual estimates. Accordingly, TMCI temperature increments, sensor spacing values, optical drift estimates, and lifetime projections are discussed only as case-specific screening-level hypotheses unless directly validated in the cited literature. Five research gaps are identified: standardized multi-sensor TMCI validation, aging-corrected material and solder fatigue databases, long-term qualification of thermally conductive nanocomposites, SFH-specific validation of physics-informed digital twins, and integrated multi-failure testing. The contribution of this article is therefore primarily structural and agenda setting: it clarifies what is supported by direct evidence, what is transferred from adjacent domains, and what remains to be validated before robust SFH-level reliability guidance can be established. Full article

Changes in urban form strongly affect surface thermal conditions, yet long-term quantitative assessments of this relationship, particularly the role of ventilation resistance, remain limited. To address this gap, this study integrates XGBoost, SHapley Additive explanations (SHAP), and multi-scale geographically weighted regression (MGWR) to examine how six morphological, ecological, and human-activity factors influence land surface temperature (LST) in Kaifeng City. The results indicate three main findings. First, LST increased significantly from 1986 to 2024, while interannual variability declined, indicating a gradual reduction in regional thermal fluctuations. Second, NTL was consistently the dominant indicator across the five representative years, while BF and NTL together captured the effects of urban expansion and intensified human activity. Third, FAD coefficients were more spatially heterogeneous in urban fringe areas than in the urban core. In 2020, the dispersion of FAD coefficients in fringe areas was 2.74 times greater than that in the central area, indicating stronger spatial differentiation in ventilation-related morphological constraints during urban expansion. Although FAD made only a modest contribution to overall predictive accuracy, it provided supplementary diagnostic information not captured by conventional density indicators and showed nonlinear, directional, and spatially heterogeneous responses. Compared with previous studies that mainly examined short-term or single-dimensional relationships between urban morphology and LST, this study integrates building densification, ventilation-related morphological resistance, ecological conditions, and human activity intensity into a long-term LST-driver framework, providing evidence to support heat-risk management during urban regeneration and outward expansion. 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

The impact of force field models on the thermal and mechanical characteristics of polyimides was comprehensively examined for the first time. Polyimides (PI) are heterocyclic polymers with outstanding thermal and chemical stabilities and excellent dielectric properties. In this study, we used all-atom molecular dynamics (MD) simulations to examine how the flexibility of the dianhydride fragment affects the thermal and mechanical properties of three polyimides: PMDA-ODA, ODPA-ODA, and R-ODA. The considered polyimides have different dianhydride fragments based on pyromellitic acid (PMDA), tetracarboxylic acid diphenyl oxide (ODPA) and 1,3-bis(3′,4-dicarboxyphenoxy)benzene acid (R), with a constant diamine: 4,4′-oxydianiline (ODA). Models were built using five classical force fields (OPLS-AA, Amber/GAFF, Gromos, Charmm/CGenFF, and UFF). For each polyimide, eight models were generated using different force fields and charge schemes: (i) OPLS-AA with 1.14*CM1A charges, (ii) OPLS-AA with HF/6-31G* (RESP) charges, (iii) GAFF with AM1-BCC charges, (iv) GAFF with HF/6-31G* (RESP) charges, (v) CGenFF (version 4.6) with native charges, (vi) CGenFF (version 5.0) with native charges, (vii) Gromos54a7 with native charges, and (viii) UFF with QEq charges. The difference in the chemical structures of the polyimide repeating unit leads to differences in the thermodynamic and kinetic flexibilities that affect the thermal and mechanical properties. Simulations of glass transition temperatures (T_g) for three polyimides PMDA-ODA, ODPA-ODA, and R-ODA mostly replicate the experimental order T_g(PMDA-ODA) > T_g(ODPA-ODA) > T_g(R-ODA), except for the CGenFF (version 4.6) force field. The experimental density ratio ρ(PMDA-ODA) > ρ(ODPA-ODA) > ρ(R-ODA) is most accurately replicated by OPLS-AA (RESP) and CGenFF (version 5.0) polyimide models. The coefficients of thermal expansion (CTE) correspond with the experimental trend, exhibiting an increase in the following order: PMDA-ODA < ODPA-ODA < R-ODA. Gromos54a7 precisely delineates both the ratio and absolute values CTE for all polymers. OPLS-AA (RESP), OPLS-AA (CM1A), CGenFF (version 4.6), and UFF (QEq) models replicate PMDA-ODA’s CTE, while GAFF (RESP) and GAFF (AM1-BCC) models replicate ODPA-ODA and R-ODA CTE values. The ratio between the simulated values of Young’s modulus, yield strength, and strain-hardening modulus followed the sequence PMDA-ODA > ODPA-ODA > R-ODA for the OPLS-AA (RESP) and CGenFF (version 5.0) models. Full article

As semiconductor packaging technology evolves from two-dimensional to three-dimensional integration, the through-glass via (TGV) technique, as a core interconnect method in advanced packaging, is emerging as a strong candidate to replace through-silicon vias (TSVs) and plated through-holes (PTHs) in organic substrates. Glass substrates offer excellent electrical insulation, low dielectric loss, tunable thermal expansion coefficients, and the potential for large-scale panel-level manufacturing. However, issues related to TGV hole quality, metallization uniformity, and thermomechanical reliability remain key bottlenecks limiting their large-scale industrialization. This investigation provides a comparative review of non-laser and laser machining for TGVs to address the above problems. First, the technical background and core advantages of TGVs are outlined. Second, this study details non-laser processing methods, including sandblasting erosion, mechanical drilling, the photosensitive glass method, electrochemical discharge machining (ECDM), deep reactive ion etching (DRIE), and others. Third, laser processing methods, covering laser ablation drilling, laser-induced deep etching (LIDE), femtosecond laser-assisted wet etching and others, are given focus. Moreover, this study analyzes typical applications of TGVs in 3D/2.5D packaging, MEMS devices, optoelectronic integration, and others. In addition, the machining processes of non-laser and laser-based TGVs, such as mechanical machining, ECDM, and LIDE, are compared, and key process challenges, technical trade-offs, and reliability failure mechanisms are discussed. Finally, this review looks ahead to future trends, aiming to provide a systematic technical reference for researchers in the TGV field. Full article

Under extreme steady-state temperature gradients, external thermal insulation composite systems (ETICSs) are prone to thermal deformation, which can cause mortar cracking, hollowing, and even delamination and detachment of insulation boards, thus degrading building envelope performance and threatening structural and personal safety. In this study, a combined method of numerical simulation using ANSYS software and experimental testing was adopted to investigate the thermal deformation characteristics of three commonly used insulation materials: Expanded Polystyrene (EPS), Extruded Polystyrene (XPS), and Polyurethane (PU). The effects of temperature difference from 10 °C to 30 °C, insulation board thickness from 30 mm to 100 mm, and surface mortar thickness from 5 mm to 10 mm on strain distribution and deformation mechanism were systematically analyzed. Experimental validation showed good agreement with the simulation results, quantified by an estimated relative error of less than 15% across the investigated insulation thicknesses and steady-state temperature conditions. The results indicate that the strains of EPS, XPS, and PU boards all increase significantly as the temperature difference across the board rises. Under outdoor temperatures of 30 °C, 40 °C and 50 °C with a constant indoor temperature of 20 °C, the thickness-direction strain at the EPS–mortar interface increases by approximately 35% when the temperature difference increases from 10 °C to 30 °C. Increasing both insulation board thickness and mortar protective layer thickness effectively reduces thermal deformation. Specifically, when the EPS board thickness increases from 30 mm to 100 mm, the thickness-direction strain decreases by approximately 73%; and when the mortar thickness increases from 5 mm to 10 mm, the interfacial strain decreases by approximately 32%. Due to differences in linear expansion coefficients, the three insulation materials exhibit distinctly different thermal deformation behaviors, with the thickness-direction strain following the order EPS > XPS > PU. These findings provide a theoretical basis and data support for material selection, structural optimization, and safety design of external wall insulation systems. Full article

Thermal/environmental barrier coating (T/EBC) protects ceramic matrix composites (CMC) from environmental corrosion and provides thermal insulation simultaneously. As a newly developed TBC material, GdPO₄ has attracted much attention due to its low thermal conductivity, but its relatively high thermal expansion coefficient (TEC) limits the application in the T/EBC system. In this study, Yb-doped GdPO₄ with properties desirable for the T/EBC system is proposed. The high-temperature stability and mechanical and thermophysical properties of Gd_1−xYb_xPO₄ (x = 0, 0.125, 0.25, 0.375, 0.5, 0.625, 0.75, 0.875 and 1) were studied, and the mechanism for doping modification was fully explained. Gd_0.75Yb_0.25PO₄ with Young’s modulus of 82 GPa and thermal conductivity of 1.01 W·m⁻¹·K⁻¹ is considered to have the most desirable properties. Compared with GdPO₄, the TEC of Gd_0.75Yb_0.25PO₄ (6.3 × 10⁻⁶ K⁻¹) is reduced by ~39%, and the fracture toughness is improved by ~30%. Therefore, Gd_0.75Yb_0.25PO₄ is considered to be suitable for usage as a T/EBC material. Full article

Boron carbide (B₄C) holds significant application potential in the fields of lightweight, high-hardness protective and high-end wear-resistant components due to its low density and exceptional hardness. However, its strong covalent bonding leads to low sintering activity and weak grain-boundary cohesion, resulting in high brittleness and crack sensitivity. These inherent properties make it difficult to achieve simultaneous full densification and toughness enhancement, severely limiting the reliability of B₄C under complex service conditions. Although diamond is an attractive reinforcement because of its high elastic modulus and low coefficient of thermal expansion, the simultaneous realization of densification, graphitization suppression, and fracture-resistance improvement in diamond/B₄C composites remains insufficiently understood. In this study, diamond particles were introduced into the B₄C matrix and consolidated by rapid high-temperature and high-pressure (HTHP) sintering to synergistically promote densification and fracture toughening. The effects of sintering temperature and diamond content on phase evolution, densification, microstructure, and mechanical properties were systematically investigated, and the associated toughening mechanisms were analyzed. The results indicate that the hardness generally increases with rising sintering temperature and diamond content. The primary toughening mechanisms are identified as the pull-out of diamond particles and crack deflection induced by residual stresses generated during the cooling process. Although the composite with 20 wt.% diamond exhibits higher hardness, it also experiences severe macroscopic cracking. The composite with 10 wt.% diamond sintered at 1450 °C under 5.3 GPa for 4 min exhibits the optimal balance of properties, achieving a relative density of 98.85%, a Vickers hardness of 40.72 GPa, and a fracture toughness of 9.20 MPa·m^1/2. This work confirms the effectiveness of combining diamond reinforcement with HTHP sintering in simultaneously achieving densification and toughening of B₄C-based composites, providing a new pathway for developing high-performance lightweight protective ceramics. Full article