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β-Yb2Si2O7 is a promising environmental barrier coating ( EBC) material and recently attracted attention for its damage tolerance. To investigate the mechanisms of its damage tolerance and possible plasticity, dense β-Yb2Si2O7 sample was synthesized by in situ reaction/hot-pressing method, and its mechanical properties were measured from room to high temperatures. The low magnitudes of hardness to Young's modulus ratio HV /E, shear modulus to bulk modulus ratio G/B, and high fracture toughness to strength ratio KIC /σ provide evidences of damage tolerance of β-Yb2Si2O7. β-Yb2Si2O7 exhibits extensive plastic deformation in Hertzian contact tests at both room and high temperatures. Transmission electron microscopy ( TEM) observations show that the deformation mechanisms are different at low and high temperatures. Deformation twinning and parallel dislocation arrangement occur in plastic deformation at room temperature. Above the brittle-to-ductile transition temperature (between 1200°C and 1300°C), plastic deformation brings out extensive slip and climb of dislocations, while twinning is seldom observed. Measurement of temperature-dependent dynamic Young's modulus demonstrates excellent elastic stiffness retention up to 1300°C. [ABSTRACT FROM AUTHOR]

Niobium aluminum carbide ( Nb4 AlC3), as a member of the MAX phases, can retain its stiffness and strength up to over 1400°C. However, its applications are limited due to its poor oxidation resistance at high temperatures. In this work, silicon pack cementation has been applied to improve the oxidation resistance of Nb4 AlC3. After Si pack cementation at 1200°C for 6 h, a dense and uniform silicide coating which was mainly composed of NbSi2 and SiC and well bonded to the matrix was successfully formed on the surface of Nb4 AlC3. The Si pack cemented Nb4 AlC3 shows excellent oxidation resistance up to 1200°C due to the formation of protective Al2 O3 layer. The oxidation kinetics of the cemented Nb4 AlC3 obey parabolic law all the way to up to 1200°C, and the parabolic rate constants of cemented Nb4 AlC3 are in the same order of magnitude as those of Ti3 AlC2 in the temperature range 1000°C-1200°C. However, the oxidation of the cemented Nb4 AlC3 was accelerated after oxidation at 1300°C for about 15 h due to the formation of NbAlO4. [ABSTRACT FROM AUTHOR]

Crystallized Lu- Si- O- N phases were believed to be the grain-boundary ( GB) phases that might provide Si3 N4 with excellent high-temperature mechanical properties. However, little is known about the intrinsic properties, as well as the synthesis, of the Lu- Si- O- N ceramics. This work reveals the reaction paths of heating Lu2 O3, SiO2, and Si3 N4 powder mixtures (with the stoichiometry of 4:0.96:1) from room temperature to 1600°C. Thereafter, dense Lu4 Si2 O7 N2 samples are synthesized by in situ reaction/hot-pressing method, and the mechanical properties at room temperature and elevated temperatures are reported for the first time. The Lu4 Si2 O7 N2 samples show significant high-temperature mechanical properties, such as the elastic stiffness remains 77% from room temperature to 1500°C; and bending strength keeps 93% from room temperature to 1400°C. The present results shine a light on Lu4 Si2 O7 N2 as a promising target GB phase for the optimization of high-temperature mechanical properties of Si3 N4. [ABSTRACT FROM AUTHOR]

Ti3 AlC2 has low density, high elastic modulus, quasi-ductility, and excellent oxidation resistance. However, its relatively low strength needs to be improved. In this study, dense Ti3 AlC2- Y4 Al2 O9 composites (containing 2.5, 5, and 7.5 wt% Y4 Al2 O9) were synthesized by hot pressing/solid-liquid reaction using Ti, Al, C, and Y2 O3 as initial materials. We investigated the in situ formation process of Y4 Al2 O9, and studied the change of microstructure and optimization of mechanical properties of the Ti3 Al C2- Y4 Al2 O9 composites. The grain size and aspect ratio of Ti3 Al C2 grains are significantly reduced in Ti3 Al C2- Y4 Al2 O9 composites, which is the source of higher strength from room temperature to elevated temperatures. The Ti3 Al C2-5 wt% Y4 Al2 O9 composite shows better optimization in its mechanical properties than other studied composites. In addition, there is an improvement in strength without debit in toughness of the composite. [ABSTRACT FROM AUTHOR]

Titanium diboride ( TiB2) was successfully hot-pressed at 1500°C using titanium aluminum carbide ( Ti3 AlC2) as a sintering aid. The mechanisms for the improved sinterability of TiB2 by the addition of Ti3 AlC2 involve, first, the Al coming from the decomposition of Ti3 AlC2 can eliminate the oxide layer on the surface of TiB2; second, the TiC x (also from the decomposition of Ti3 AlC2) has a positive influence on the densification of TiB2 due to its plasticity at high temperatures. TEM observations reveal that the interface between TiB2 and TiC x is coherent and strong, free of amorphous layers and oxide phases. An optimized composition of TiB2-10 wt% Ti3 AlC2 was obtained with the unique combination of mechanical properties, including the elastic modulus of 567 GPa, the fracture toughness of 4.8 MPa·m1/2, the flexural strength of 711 MPa, and the hardness of 25 GPa. [ABSTRACT FROM AUTHOR]

Two new MAX compounds, ( Cr2/3 Ti1/3)3 AlC2 and ( Cr5/8 Ti3/8)4 AlC3, were successfully synthesized by hot-pressing elemental powders at 1500°C for 1 h under 30 MPa in a flowing argon atmosphere. Their crystal structures were indentified and characterized by X-ray diffraction and transmission electron microscopy analysis. ( Cr2/3 Ti1/3)3 AlC2 and ( Cr5/8 Ti3/8)4 AlC3 have the same crystal structures with the well-characterized Ti3 AlC2 and Ti4 AlN3, respectively. [ABSTRACT FROM AUTHOR]

Improving the high-temperature strength and stiffness of Ti3 SiC2 is the task of many investigations. However, methods for high-temperature strengthening have not been established although various ways are applicable to enhance the room-temperature mechanical properties of Ti3 SiC2. In this work, we report that significant strengthening was realized at both room and high temperatures by incorporating a small amount of W into Ti3( Si, Al) C2. The onsite temperature for the rapid degradation of stiffness and strength moved more than 150°C upward to over 1200°C. The flexural strength of 5 at.% W-doped Ti3( Si, Al) C2 is 632.9 MPa at RT and 285 MPa at 1200°C, being 176% and 170% of those for baseline material, respectively. [ABSTRACT FROM AUTHOR]

A new compound, Ti5 Al2 C3, is identified in the bulk sample prepared by reactive hot pressing a mixture of Ti, Al and graphite powders with a nominal molar ratio of Ti: Al: C = 5:2.15:2.78 at 1580°C for 1 h. This compound follows the crystal structure of other MAX phases. The lattice parameters are a = 0.3038 nm, c = 3.2261 nm, and the atomic positions are Ti1 at 4 f (1/3, 2/3, 0.0208), Ti2 at 4 f (1/3, 2/3, 0.1778), Ti3 at 2 d (2/3, 1/3, 0.25), Al at 4 e (0, 0, 0.1035), C1 at 2 a (0, 0, 0), and C2 at 4 e (0, 0, 0.2102). [ABSTRACT FROM AUTHOR]

RE2SiO5 with low thermal conductivity, compatible thermal expansion coefficients and excellent high-temperature reliability in harsh environments are excellent candidates as advanced environmental/thermal barrier coating materials for high-efficiency gas turbine engines. A series of rare earth silicates (HoxY1-x)2SiO5 are designed and their properties are comprehensively investigated in this paper. Through doping Ho into Y2SiO5, the thermal conductivity of Y2SiO5 is significantly decreased and the thermal expansion coefficient is also optimized closer to Si-based ceramics. High-temperature elastic stiffness and bending strength are increased with the enhancing of Ho content. Most important, doping Ho element provides (HoxY1-x)2SiO5 with tunable luminescence characteristic. (HoxY1-x)2SiO5 exhibit green, to yellow-green, then to orange-red luminescence color with increased Ho concentration. The results show that they can be used as damage self-monitoring environmental/thermal barrier coating materials for Si-based ceramics. [ABSTRACT FROM AUTHOR]

Crystallized Lu- Si- O- N phases were believed to be the grain-boundary ( GB) phases that might provide Si3 N4 with excellent high-temperature mechanical properties. However, little is known about the intrinsic properties, as well as the synthesis, of the Lu- Si- O- N ceramics. This work reveals the reaction paths of heating Lu2 O3, SiO2, and Si3 N4 powder mixtures (with the stoichiometry of 4:0.96:1) from room temperature to 1600°C. Thereafter, dense Lu4 Si2 O7 N2 samples are synthesized by in situ reaction/hot-pressing method, and the mechanical properties at room temperature and elevated temperatures are reported for the first time. The Lu4 Si2 O7 N2 samples show significant high-temperature mechanical properties, such as the elastic stiffness remains 77% from room temperature to 1500°C; and bending strength keeps 93% from room temperature to 1400°C. The present results shine a light on Lu4 Si2 O7 N2 as a promising target GB phase for the optimization of high-temperature mechanical properties of Si3 N4. [ABSTRACT FROM AUTHOR]

Global warming and nitrogen (N) deposition are important factors impacting soil carbon (C) and N cycling. Termites are important ecosystem engineers that can also strongly affect C and N cycling, potentially in interaction with warming and N deposition. In addition, non-additive effects that magnify or reduce their impacts on soil element cycles may occur when termite nests and adjacent soils are mixed due to their divergent properties but this has not been investigated. Here, we collected termite nests and trails built in wood (“termite nest soils”) and adjacent control soils in forests at Lu Mountain (Jiangxi, China) to investigate effects of termites, warming, and N deposition on C and N processes. We measured CO 2 emissions, N 2 O emissions, net N mineralization, and net nitrification when soils were incubated at different temperatures (15 °C, 25 °C, or 35 °C) and levels of N deposition (control vs. 4 g N m − 2 ). Termite nest soils were characterized by higher dissolved organic C and CO 2 emissions. CO 2 emissions decreased with N addition and increased with temperature. N 2 O emissions increased with N deposition and increased with temperature, especially in termite nest soils and mixed soils. Net N mineralization rates increased with temperature but increases were smaller and more gradual in control and mixed soils than in termite soils. Mixing termite nest soils and control soils imposed synergistic (N mineralization: up to 57% higher than expected; nitrification: up to 170% higher; N 2 O emissions without N addition: 18% higher) and antagonistic (CO 2 emissions: 7% lower; N 2 O emissions with N addition: 28% lower) mixing effects, indicating termite impacts on soil C and N cycling might be under- and over-estimated, respectively, based on each soil alone. In light of the remarkable abundance of termites, the effects of mixing termite nest soils and the control soils on soil C and N cycling should be considered in the context of global change. [ABSTRACT FROM AUTHOR]

Chemical-looping combustion (CLC) is a promising technology that utilizes metal oxides as oxygen carriers for the combustion of fossil fuels to CO 2 and H 2 O, with CO 2 readily sequestrated after the condensation of steam. Thermally stable and reactive metal oxides are desirable as oxygen carrier materials for the CLC processes. Here, we report the performance of Cu-based mixed oxides derived from hydrotalcite (also known as layered double hydroxides) precursors as oxygen carriers for the combustion of solid fuels. Two types of CLC processes were demonstrated, including chemical looping oxygen uncoupling (CLOU) and in situ gasification (iG-CLC) in the presence of steam. The Cu-based oxygen carriers showed high performance for the combustion of two solid fuels (a lignite and a bituminous coal), maintaining high thermal stability, fast reaction kinetics, and reversible oxygen release and storage over multiple redox cycles. Slight deactivation and sintering of the oxygen carrier occurred after redox cycles at an very high operation temperature of 985 °C. We expect that our material design strategy will inspire the development of better oxygen carrier materials for a variety of chemical looping processes for the clean conversion of fossil fuels with efficient CO 2 capture., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

Objective: To evaluate the efficacy on hemiplegic spasticity after cerebral infarction treated with plum blossom needle tapping therapy at the key points and Bobath therapy., Methods: Eighty patients were collected, in compliance with the inclusive criteria of hemiplegic spasticity after cerebral infarction, and randomized into an observation group and a control group, 40 cases in each one. In the control group, Bobath manipulation therapy was adopted to relieve spasticity and the treatment of 8 weeks was required. In the observation group, on the basis of the treatment as the control group, the tapping therapy with plum blossom needle was applied to the key points, named Jianyu (LI 15), Jianliao (LI 14), Jianzhen (SI 9), Hegu (LI 4), Chengfu (BL 36), Zusanli (ST 36), Xiyangguan (GB 33), etc. The treatment was given for 15 min each time, once a day. Before treatment, after 4 and 8 weeks of treatment, the Fugl-Meyer assessment (FMA) and Barthel index (BI) were adopted to evaluate the motor function of the extremity and the activity of daily life in the patients of the two groups separately. The modified Ashworth scale was used to evaluate the effect of anti-spasticity., Results: In 4 and 8 weeks of treatment, FMA: scores and BI scores were all significantly increased as compared with those before treatment in the two groups: (both P<0. 05). The results in 8 weeks of treatment in the observation group were significantly better than those in the control group (all P<0. 05). In 4 and 8 weeks of treatment, the scores of spasticity state were improved as compared with those before treatment in the patients of the two groups (all P<0. 05). The result in 8 weeks of treatment in the observation group was significantly better than that in the control group (P<0. 05). In 8 weeks of treatment, the total effective rate of anti-spasticity was 90. 0% (36/40) in the observation group, better than 75. 0% (30/40) in the control group (P<0. 05)., Conclusion: The tapping therapy with plum blossom needle at the key points combined with Bobath therapy effectively relieves hemiplegic spasticity in the patients of cerebral infarction and improves the motor function of extremity and the activity of daily life.

We developed a technique to observe and characterize a novice real-time-strategy (RTS) player's mental model as it shifts with experience. We then tested this technique using an off-the-shelf RTS game, EA Games Generals. Norman defined mental models as, "an internal representation of a target system that provides predictive and explanatory power to the operator." In the case of RTS games, the operator is the player and the target system is expressed by the relationships within the game. We studied five novice participants in laboratory-controlled conditions playing a RTS game. They played Command and Conquer Generals for 2 h per day over the course of 5 days. A mental model analysis was generated using player dissimilarity-ratings of the game's artificial intelligence (AI) agents analyzed using multidimensional scaling (MDS) statistical methods. We hypothesized that novices would begin with an impoverished model based on the visible physical characteristics of the game system. As they gained experience and insight, their mental models would shift and accommodate the functional characteristics of the AI agents. We found that all five of the novice participants began with the predicted physical-based mental model. However, while their models did qualitatively shift with experience, they did not necessarily change to the predicted functional-based model. This research presents an opportunity for the design of games that are guided by shifts in a player's mental model as opposed to the typical progression through successive performance levels.