Search Results (16)

The generalized planar fault energies of 1/2<110] and 1/6<112] slip directions on {111} planes in $\gamma$-TiAl at temperatures up to 1500 K were predicted through first-principles calculations and quasi-harmonic approximation. The obtained unstable stacking and twinning fault (USF and UTF) energies, as well as superlattice intrinsic and extrinsic stacking fault (SISF and SESF) energies, are consistent with existing theoretical data. Results show that the USF, UTF, SISF, and SESF energies for both slip directions decrease overall as temperature increases. The effect of temperature on the 1/2<110] ordinary dislocation and 1/6<112] order twinning in $\gamma$-TiAl is further analyzed generalized planar fault energies. It is demonstrated that the nucleation of ordinary dislocation and twinning dislocations becomes more favorable with increasing temperature. Furthermore, it is shown that order twinning in $\gamma$-TiAl is more likely to occur at crack tips or grain boundaries, and its twinnability is enhanced at elevated temperatures. Full article

Tight sandstone gas reservoirs, characterized by low porosity (typically < 10%) and ultra-low permeability (commonly < 0.1 × 10⁻³ μm²), represent a critical transitional resource in global energy transition, accounting for over 60% of total natural gas production in regions such as North America and Canada. In the northern Tianhuan Depression of the Ordos Basin, the Permian He 8 Member (He is the abbreviation of Shihezi) of the Shihezi Formation serves as one of the primary gas-bearing intervals within such reservoirs. Dominated by quartz sandstones (82%) with subordinate lithic quartz sandstones (15%), these reservoirs exhibit pore systems primarily supported by high-purity quartz and rigid lithic fragments. Diagenetic processes reveal sequential cementation: early-stage quartz cementation provides a framework for subsequent lithic fragment cementation, collectively resisting compaction. Depositionally, these sandstones are associated with fluvial-channel environments, evidenced by a sand-to-mud ratio of ~5.2:1. Pore structures are dominated by intergranular pores (65%), followed by dissolution pores (25%) formed via selective leaching of unstable minerals by acidic fluids in hydrothermal settings, and minor intragranular pores (10%). Authigenic clay minerals, predominantly kaolinite (>70% of total clays), act as the main interstitial material. Reservoir properties average 7.01% porosity and 0.5 × 10⁻³ μm² permeability, defining a typical low-porosity, ultra-low-permeability system. Vertically stacked sand bodies in the He 8 Member display large single-layer thicknesses (5–12 m) and moderate sealing capacity (caprock breakthrough pressure > 8 MPa), hosting gas–water mixed-phase occurrences. Rock mechanics experiments demonstrate that fractures enhance permeability by >60%, significantly controlling reservoir heterogeneity. Full article

Ultra-thin PTCDI-C8 films are vapor-deposited under ultra-high vacuum (UHV) conditions onto surfaces of p- or n-doped GaN(0001) samples. The X-ray photoelectron spectroscopy (XPS) results reveal a lack of strong chemical interaction between the PTCDI-C8 molecule and the substrate. Changes in the electronic structure of the substrate or the adsorbed molecules due to adsorption are not noticed at the XPS spectra. Work function changes have been measured as a function of the film thickness. The position of the HOMO level for films of thicknesses 3.2–5.5 nm has been determined. Energy diagrams of the interface between p- and n-type GaN(0001) substates and the PTCDI-C8 films are proposed. The fundamental molecular building blocks of the PTCDI-C8 films on GaN(0001), assembled by self-organization, have been identified. They are rows of PTCDI-C8 molecules stacked in “stand-up” positions in reference to the substrate, supported by the π–π bonds which are formed between the molecular cores of the molecules and monomolecular layers constituted by rows which are tilted in reference to the layer plane. The layers are epitaxially oriented. The epitaxial relation between the rows and the crystallographic directions of the substrate are determined. A model of the PTCDI-C8 film’s growth on GaN(0001) substrate is proposed. The 3D islands of PTCDI-C8 molecules formed on the substrate surface during film deposition are thermodynamically unstable. The Volmer–Weber type of growth observed here is a kinetic effect. Rewetting processes are noticeable after film aging at room temperature or annealing at up to 100 °C. Full article

The transient responses of distributed energy resources (DERs) in a microgrid are dynamically correlated in spatial and temporal dimensions. Hence, the transient stability prediction in microgrids would require an effective modeling of time-varying correlations and the mining of spatial–temporal features of electrical data. This paper proposes a refined DER-level transient stability prediction method for microgrids considering the time-varying spatial–temporal correlations of DERs. First, the spatial–temporal dynamic correlation of DERs was extracted and modeled by an attention-based mechanism. Then, a spatial–temporal graph convolution network was proposed to predict the dynamics of unstable DERs and the instability severity trend in a microgrid. The TSP model consisted of three parts: (1) several stacked spatial–temporal convolution modules to simultaneously mine the spatial–temporal dynamic features of microgrids, (2) an unstable DER identification module to predict the microgrid system stability and identify unstable DERs, and (3) an instability severity trend prediction module for DERs in a microgrid. The test results on a realistic 16-bus 10-DER microgrid demonstrated that the proposed prediction method possessed the desirable reliability and interpretability and outperformed the state-of-the-art baselines in unstable DER identifications and DER instability severity trend predictions. Full article

The proton battery has facilitated a new research direction for technologies related to fuel cells and energy storage. Our R&D team has developed a prototype of a proton battery stack, but there are still problems to be solved, such as leakage and unstable power generation. Moreover, it is unlikely that the multiple important physical parameters inside the proton battery stack can be measured accurately and simultaneously. At present, external or single measurements represent the bottleneck, yet the multiple important physical parameters (oxygen, hydrogen, voltage, current, temperature, flow, and humidity) are interrelated and have a significant impact on the performance, life, and safety of the proton battery stack. This research uses micro-electro-mechanical systems (MEMS) technology to develop a micro oxygen sensor and integrates the six-in-one microsensor that our R&D team previously developed in order to improve sensor output and facilitate overall operation by redesigning the incremental mask and having this co-operate with a flexible board for sensor back-end integration, completing the development of a flexible seven-in-one (oxygen, hydrogen, voltage, current, temperature, flow, and humidity) microsensor. Full article

In this paper, an Ab-initio study was employed to study the properties of interfaces of Al₃Y|Al. The interface strength, shear strength, structural stability, electronic density, bonding characteristics, stacking fault energy, and plasticity were all investigated. The interface with the stacking style of ABab or CBAcba has the greatest interface strength. The Al₃Y(111)|Al(111) interface has the highest tensile stress of 13.39 GPa for rigid stretching; and 9.39 GPa for relaxation stretching. In the stretching process, the Al₃Y(111)|Al(111) interface is prone to break on the Al₃Y side. However, the Al₃Y(010)|Al(010) and Al₃Y(110)|Al(110) interface systems tend to fracture at the interface and Al side, respectively. Moreover, the differential charge density, electron localization function, and partial density of states (PDOS) demonstrate the newly formed chemical bonds at the interface, and the chemical bonds were formed by s-p or s-p-d hybrid orbitals. According to the Rice ratio and shear stress, these interfaces were found to be plastic and the Al₃Y(111)|Al(111) interface has the best plasticity. This is significant because the formed interfaces are all advanced structure materials, which can be potentially used in automobile and aeronautical fields, even in some special industries. Full article

The ideal mechanical shear properties and sliding characteristics of c-ZrO₂(001)/α-Al₂O₃($1\overline{1}02$) interfaces are examined through simulated shear deformations using first-principles calculations. We investigate three types of interface models, abbreviated as O-, 2O-, and Zr- models, when shear displacements are applied along the <$1\overline{1}01$> and <$11\overline{2}0$> directions of their Al₂O₃ lattice. The theoretical shear strength and unstable stacking energy of the ZrO₂/Al₂O₃ interfaces are discussed. In the process of the ZrO₂/Al₂O₃ interfacial shear deformation, we find that the sliding of the ZrO₂ atomic layers, accompanied by the shifting of Zr atoms and Al atoms near the interface, plays a dominant role; in addition, the ZrO₂/Al₂O₃ interfaces fail within the ZrO₂ atomic layer. Among the three models, the O- model exhibits the strongest shear resistance; whereas the Zr- model is the most prone to slip. Furthermore, their tensile and shear strengths are compared; moreover, their potential applications are provided. Full article

The elastic constants, core width and Peierls stress of 30° partial dislocation in germanium has been investigated based on the first-principles calculations and the improved Peierls–Nabarro model. Our results suggest that the predictions of lattice constant and elastic constants given by LDA are in better agreement with experiment results. While the lattice constant is overestimated at about 2.4% and most elastic constants are underestimated at about 20% by the GGA method. Furthermore, when the applied deformation is larger than 2%, the nonlinear elastic effects should be considered. And with the Lagrangian strains up to 8%, taking into account the third-order terms in the energy expansion is sufficient. Except the original $\gamma$—surface generally used before (given by the first-principles calculations directly), the effective γ—surface proposed by Kamimura et al. derived from the original one is also used to study the Peierls stress. The research results show that when the intrinsic−stacking−fault energy (ISFE) is very low relative to the unstable−stacking−fault energy (USFE), the difference between the original $\gamma$—surface and the effective $\gamma$—surface is inapparent and there is nearly no difference between the results of Peierls stresses calculated from these two kinds of $\gamma$—surfaces. As a result, the original $\gamma$—surface can be directly used to study the core width and Peierls stress when the ratio of ISFE to the USFE is small. Since the negligence of the discrete effect and the contribution of strain energy to the dislocation energy, the Peierls stress given by the classical Peierls–Nabarro model is about one order of magnitude larger than that given by the improved Peierls–Nabarro model. The result of Peierls stress estimated by the improved Peierls–Nabarro model agrees well with the 2~3 GPa reported in the book of Solid State Physics edited by F. Seitz and D. Turnbull. Full article

The relative stability of polymorphs and their electronic structure was investigated for II-IV-V${}_2$ materials by using first-principles density functional theory calculations. Our calculation results show that, for Zn-, Cd-, and Be-containing compounds, nitrides favor the 2H polymorph with AB stacking sequence; however, phosphides, arsenides, and antimonides are more stable in the 3C polymorph with the ABC stacking sequence. The electronic band gap of materials was calculated by using hybrid density functional theory methods, and then materials with an ideal band gap for photovoltaic applications were chosen. The experimental synthesis of the screened materials is reported, except for CdSiSb₂, which was found to be unstable in our calculation. The absorption coefficient of the screened materials, especially ZnGeAs₂, was high enough to make thin-film solar cells. The higher stacking fault energy in ZnGeAs₂ than the others is consistent with the larger formation energy difference between the 2H and 3C polymorphs. Full article

Solid Oxide Fuel Cell (SOFC) technology is of high interest for stationary decentralized generation of electricity and heat in combined heat and power systems (CHP) for the residential sector. Application scenarios for SOFC systems in an electricity-regulated mode play an important role, especially in places where an electrical grid connection is not available or rather unstable. The advantages of SOFC systems are the high fuel flexibility and the high efficiencies also under partial load operation compared to other decentralized power generation technologies. Due to the long, energy-consuming system heat-up and the limited partial load capability, SOFC systems do not reach the performance of conventional power generation technologies. Furthermore, stack thermal cycling is associated with power degradation and should be minimized. In this paper, the improvement of these drawbacks are investigated for hotbox-based SOFC systems in the 1 kW_el-class for residential applications. Since experimental investigations of the high-temperature systems are limited, modeling tools are established, enabling the visualization of internal system characteristics and providing the opportunity to simulate system operation in critical regions. To achieve this, a methodology for dynamic SOFC system modeling in a process engineering manner is developed based on the modeling language Modelica. A suitable approach is particularly important for modeling and simulation of the strong thermal interaction between the hot system components within the hotbox. The parametrized and validated models are used for the investigation of different dynamic effects, such as the system heat-up and the operation in low partial load points. A second reduced thermal system model aims for annual simulations of the SOFC system together with a battery to investigate the number of thermal cycles and the advantage of a hot standby operation. As a result, it is found that an adequate control of the power input at the start-up device and the cathode air flow has a high improvement potential to increase the stack heating rate and accelerate the heat-up in an energy-saving way. The hotbox-internal thermal management is identified as a crucial issue to reach low partial load points. To avoid the risk of stack cooling, lower heat losses and/or additional heat sources are of importance. Furthermore, the robustness of the tail gas oxidizer is found to be crucial for a higher load flexibility during partial load and the end of life stack operation. The annual simulation results indicate that operating the battery hybrid system with a hot standby mode requires much lower battery capacity for a high grid independence and a complete avoidance of system shutdown and associated power degradation. Full article

Automobile shredder residue (ASR) pyrolysis produces solid, liquid, and gaseous products, particularly pyrolysis oil and gas, which could be used as renewable alternative energy resources. Due to the primary pyrolysis reaction not being complete, the yield of gaseous product is low. The pyrolysis tar comprises chemically unstable volatiles before condensing into liquid. Understanding the characteristics of volatile products will aid the design and improvement of subsequent processes. In order to accurately analyze the chemical characteristics and yields of volatile products of ASR primary pyrolysis, TG–FTIR–GC/MS analysis technology was used. According to the analysis results of the Gram–Schmidt profiles, the 3D stack plots, and GC/MS chromatograms of MixASR, ASR, and its main components, the major pyrolytic products of ASR included alkanes, olefins, and alcohols, and both had dense and indistinguishable weak peaks in the wavenumber range of 1900–1400 cm⁻¹. Many of these products have unstable or weaker chemical bonds, such as =CH–, =CH2, –C=C–, and –C=CH2. Hence, more syngas with higher heating values can be obtained with further catalytic pyrolysis gasification, steam gasification, or higher temperature pyrolysis. Full article

The bonding properties of the twin boundary in polysynthetic twinned γ-TiAl crystal and the effect of interstitial alloy elements on it are investigated by first principles. Among the three different kinds of interface relationships in the γ/γ interface, the proportion of true twin boundaries is the highest because it has the lowest interfacial energy, the reason for which is discussed by local energy and three-center bond. The presence of the interstitial atoms C, N, H, and O induces the competition for domination between their affinity to host atoms and three-center bonds, which eventually influences the values of unstable stacking fault energy (USFE) and intrinsic stacking fault energy (ISFE). The relative importance of different bonding with different alloy elements is clarified based on the analysis of local energy combined with Electron Localization Function (ELF) and Quantum Theory of Atoms in Molecules (QTAIM) schemes. Full article

Using first-principles methods, we investigate the effect of Al on the generalized stacking fault energy of face-centered cubic (fcc) CrMnFeCoNi high-entropy alloy as a function of temperature. Upon Al addition or temperature increase, the intrinsic and extrinsic stacking fault energies increase, whereas the unstable stacking fault and unstable twinning fault energies decrease monotonously. The thermodynamic expression for the intrinsic stacking fault energy in combination with the theoretical Gibbs energy difference between the hexagonal close packed (hcp) and fcc lattices allows one to determine the so-called hcp-fcc interfacial energy. The results show that the interfacial energy is small and only weakly dependent on temperature and Al content. Two parameters are adopted to measure the nano-twinning ability of the present high-entropy alloys (HEAs). Both measures indicate that the twinability decreases with increasing temperature or Al content. The present study provides systematic theoretical plasticity parameters for modeling and designing high entropy alloys with specific mechanical properties. Full article

Power management systems (PMSs) are essential for the practical use of microbial fuel cell (MFC) technology, as they replace the unstable stacking of MFCs with step-up voltage conversion. Maximum-power extraction technology could improve the power output of MFCs; however, owing to the power consumption of the PMS operation, the maximum-power extraction point cannot deliver maximum power to the application load. This study proposes a practical power extraction for single MFCs, which reserves more electrical energy for an application load than conventional maximum power-point tracking (MPPT). When experimentally validated on a real MFC, the proposed method delivered higher output power during a longer PMS operation time than MPPT. The maximum power delivery enables more effective power conditioning of various micro-energy harvesting systems. Full article

The governing equation of screw dislocations in heterostructures is constructed using image method. The interface type ( $-1\le \gamma \le 1$ ) and distance between dislocation and interface h are considered in the new equation. The Peierls–Nabarro equations for screw dislocations in bulk and semi-infinite materials can be recovered when $\gamma =0$ and $\gamma =-1$ . The soft ( $\gamma <0$ ) and hard ( $\gamma >0$ ) interfaces can enhance and reduce the Peierls stress of screw dislocations near the interface, respectively. The interface effects on dislocations decrease with the increasing of distance h. The Al/TiC heterostructure is investigated as a model interface to study the unstable stacking fault energy and dislocation properties of the interface. The mismatch of lattice constants and shear modulus at the interface results in changes of the unstable stacking fault energy. Then, the changes of the unstable stacking fault energy also have an important effect on dislocation properties, comparing with $\gamma$ and h. Full article