Electrical conductivity of Nd and Ce co-doped Gd2Zr2O7 ceramics

In this study, (Gd_{1? x} Nd _x )₂(Zr_{1? x} Ce _x )₂O₇ (0 ≤ x ≤ 0.5) ceramics have been prepared by pressureless sintering at 1973 K to investigate the influence of Nd and Ce co-doping on their electrical conductivity. The electrical conductivity of the ceramics was investigated by impedance spectroscopy measurements from 723 to 1173 K over the frequency range of 20 Hz to 2 MHz in air. The measured values obey the Arrhenius relation. For each composition, the grain conductivity gradually increases with increasing temperature from 723 to 1173 K. At a given temperature, it gradually decreases with increasing neodymium and cerium contents from x = 0 to 0.3; thereafter, the grain conductivity exhibits a slight increase with further increasing neodymium and cerium contents up to x = 0.5.     

Electropulsing-induced strengthening of steel at high temperature

Electropulsing usually promotes a metastable phase to evolve towards its equilibrium state. This work reports an alternative case, where electropulsing promotes the decomposition of the stable δ-phase in duplex stainless steel at high temperature. This decomposition enables both the γ-phase and the σ-phase in the steel to survive and hence to strengthen it at high temperature. The hardness of the quenched sample with electropulsing treatment is 49.4% higher than that without electropulsing treatment. A fundamental understanding of the observation is developed.     

Very high temperature creep behavior of a single crystal Ni-based superalloy under complex thermal cycling conditions

Very high temperature thermal cycling has been performed on the single crystal superalloy MC2 to evaluate the effect of periodic overheating on creep behavior. The experiments consist of alternately performing 1 min dwell time at 1100°C and 1150°C for every 15 min during creep test at 1050°C/120 MPa. Both thermal cycling and prior γ′-rafting appear to be deleterious to the cyclic creep properties. The observed non-isothermal creep behavior is correlated with γ′-dissolution/coalescence processes, especially during overheatings where γ′ micro-rafts seem to play a significant role.     

A continuum model of deformation-twin dominant crack growth in fcc metals

A continuum model is proposed to address the effects of deformation twinning on ductile versus brittle fracture behaviour of low strain-hardening fcc metals after exhaustion of work hardening. Instead of discrete twin nucleation, a number of partial dislocations ahead of the tip exhibit themselves as twins at the final stage of failure. The crack-tip plasticity is amended for deformation twinning and the constitutive form for the flow strength of arrays of twins of the same sign is expressed as a second gradient of microrotation for their coupling. The twins not only shield the crack tip but also inhibit further dislocation emission to form a dislocation-free zone (DFZ) in the immediate vicinity of the tip. The stress fields induced by deformation twinning lead to fracture branching under Mode I loading. The model is borrowed from the conceptual model presented by Beltz et al. [Acta Mater. 44 3943 (1996)], based on the equivalence of the stresses derived from twin-based crack-tip plasticity, macroscopic plasticity and elasticity on the DFZ boundary. The DFZ size and the crack-tip shielding ratio are obtained, as well as the branching angle. The branching angle is noteworthy for low strain-hardening metals. A strong dependence of the toughness on intrinsic surface energy and hardening index is examined. The toughness reduction due to crack-tip constraints and in the ductile-to-brittle transition (DBT) temperature region is revisited and found to be in agreement with experimental observations and available predictions.     

Growth orientation of one-dimensional silicon nanowires prepared by thermal evaporation

One-dimensional silicon nanowires have been grown by thermal evaporation and their growth orientations determined by transmission electron microscopy studies. The nanowires, which are often highly curved in morphology and heavily twinned in microstructure, are crystallographically separated into several sections, each with a characteristic crystallographic orientation along the wire axis. Straight nanowires, or straight sections in a curved nanowire, are found to have non-unique crystallographic orientations when {111} twinning occurs.     

Multiple phase transitions in CuO

Electrical resistivity, thermoelectric power, magnetic susceptibility and calorimetric measurements were carried out on a single crystal of CuO. In addition the two known antiferromagnetic transitions between 210K and 230K, a new phase transition around 160K was found in CuO. The experimental results show that this new transition is related to changes in the electronic state of CuO.     

Survey of plateau behaviour in the cyclic stress-strain curve of copper single crystals

Experimental results relating to the plateau behaviour in the cyclic stress-strain (CSS) curve of copper single crystals located on different sides of the stereographic triangle are summarized. Unlike the situation for single-sliporiented crystals, the crystallographic orientation has a strong effect on the plateau behaviour in the CSS curves of double- and multiple-slip-oriented crystals. The existence or non-existence of a plateau in the CSS curves, as well as the corresponding plateau stress amplitude, depend not only on the modes and intensities of dislocation interactions among slip systems operating in the crystals but also on the slip deformation characteristics associated with crystal orientations. The plateau region in CSS curve disappears only when multiple slip plays a determining role during cyclic deformation.     

Crystallization behaviour of Al-based amorphous alloy and nanocomposites by rapid quenching

The microstructure and crystallization behaviour of melt-spun Al₈₈Ni₉Ce₂Fe₁ amorphous alloy and nanophase composites have been studied by means of X-ray diffraction, transmission electron microscopy and scanning and isothermal calorimetry. The diffraction patterns from Al₈₈Ni₉Ce₂Fe₁ amorphous alloys are diffuse, indicating a basically amorphous structure but contain two rings presumed to be associated with quenched-in nuclei. In the cases of Al₈₈Ni₉Ce₂Fe₁ nanophase composites, nanoscale precipitated particles are homogeneously dispersed in an amorphous matrix, and the crystallite diameter and volume fraction are sensitive to quenching conditions. During thermal crystallization, a two-step phase transformation occurs in the amorphous alloy and nanocomposites, which is characterized by a diffusion-controlled precipitation of nanoscale Al particles and the growth of a Al₃(Ni, Fe) nanophase prior to a Al₁₁Ce₃ nanophase. This study gives insight into structure-control for obtaining nanophases dispersed in an amorphous matrix by rapid quenching.     

The role of outcome inhibition in interference between outcomes: A contingency‐learning analogue of retrieval‐induced forgetting

Current associative theories of contingency learning assume that inhibitory learning plays a part in the interference between outcomes. However, it is unclear whether this inhibitory learning results in the inhibition of the outcome representation or whether it simply counteracts previous excitatory learning so that the outcome representation is neither activated nor inhibited. Additionally, these models tend to conceptualize inhibition as a relatively transient and cue‐dependent state. However, research on retrieval‐induced forgetting suggests that the inhibition of representations is a real process that can be relatively independent of the retrieval cue used to access the inhibited information. Consistent with this alternative view, we found that interference between outcomes reduces the retrievability of the target outcome even when the outcome is associated with a novel (non‐inhibitory) cue. This result has important theoretical implications for associative models of interference and shows that the empirical facts and theories developed in studies of retrieval‐induced forgetting might be relevant in contingency learning and vice versa.     

Self-evaluation and self-perception: The role of attention in the experience of anxiety

Abstract

Self-awareness promotes the experience of anxiety in two ways. It does so directly, by enhancing awareness of the emotional state itself, and by initiating the self-evaluation process that is necessary for anxiety to occur. It also does so indirectly, by constraining some behaviors and inhibiting others. In particular, it increases accuracy of self-perception, and, in so doing, retards the process of self-delusion. This is important, because the latter process has been shown to have a salutary effect on mental health, acting as a buffer against dysphoric states such as depression and anxiety.