In situ stress relaxation mechanism of a superelastic NiTi shape memory alloy under hydrogen charging

On account of its good biocompatibility, superelastic Ni–Ti arc wire alloys have been successfully used in orthodontic clinics. Nevertheless, delayed fracture in the oral cavity caused by hydrogen diffusion can be observed. The in situ stress relaxation susceptibility of a Ni–Ti shape memory alloy towards hydrogen embrittlement has been examined with respect to the current densities and imposed deformations. Orthodontic wires have been relaxed at different martensite volume fractions using current densities of 5, 10 and 20 A/m² at 20 °C. The in situ relaxation stress shows that, for an imposed strain at the middle of the austenite–martensite transformation, the specimen fractures at the martensite–austenite reverse transformation. However, for an imposed strain at the beginning of the austenite–martensite plateau, the stress decreases in a similar way to the full austenite structure. Moreover, the stress plateau has been recorded at the reverse transformation for a short period. For the fully martensite structure, embrittlement occurs at a higher stress value. This behaviour is attributed to the interaction between the in situ austenite phase expansion and the diffusion of hydrogen in the different volume fractions of the martensite phase, produced at an imposed strain.     

Strong interactions between hydrogen in solid solution and stress-induced martensite transformation of Ni–Ti superelastic alloy

The role of the dynamic interactions between hydrogen in a solid solution and the stress-induced martensite transformation in hydrogen embrittlement has been investigated using trained Ni–Ti superelastic alloy. In a cyclic tensile test in the stress plateau region caused by stress-induced martensite and reverse transformations after hydrogen charging, a further decrease in the critical stress for the martensite transformation is observed. In addition, the number of cycles to fracture for a trained specimen is significantly larger than that for a non-trained specimen. Since most of the charged hydrogen is preferentially trapped in defects induced by training, the hydrogen embrittlement is considerably suppressed as a result of decreasing interactions between the hydrogen and the transformation. The present results indicate that hydrogen in a solid solution more strongly interacts with the stress-induced martensite transformation than hydrogen trapped in defects, thereby further enhancing the hydrogen embrittlement related to phase transformations.     

First interactions between hydrogen and stress-induced reverse transformation of Ni–Ti superelastic alloy

The first dynamic interactions between hydrogen and the stress-induced reverse transformation have been investigated by performing an unloading test on a Ni–Ti superelastic alloy subjected to hydrogen charging under a constant applied strain in the elastic deformation region of the martensite phase. Upon unloading the specimen, charged with a small amount of hydrogen, no change in the behaviour of the stress-induced reverse transformation is observed in the stress-strain curve, although the behaviour of the stress-induced martensite transformation changes. With increasing amount of hydrogen charging, the critical stress for the reverse transformation markedly decreases. Eventually, for a larger amount of hydrogen charging, the reverse transformation does not occur, i.e. there is no recovery of the superelastic strain. The residual martensite phase on the side surface of the unloaded specimen is confirmed by X-ray diffraction. Upon training before the unloading test, the properties of the reverse transformation slightly recover after ageing in air at room temperature. The present study indicates that to change the behaviour of the reverse transformation a larger amount of hydrogen than that for the martensite transformation is necessary. In addition, it is likely that a substantial amount of hydrogen in solid solution more strongly suppresses the reverse transformation than hydrogen trapped at defects, thereby stabilising the martensite phase.     

Falling on sensitive ears: constraints on bilingual lexical activation

Abstract— Spoken word recognition is characterized by multiple activation of sound patterns that are consistent with the acoustic-phonetic input. Recently, an extreme form of multiple activation was observed: Bilingual listeners activated words from both languages that were consistent with the input. We explored the degree to which bilingual multiple activation may be constrained by fine-grained acoustic-phonetic information. Ina head-mounted eyetracking experiment, we presented Spanish-English bilinguals with spoken Spanish words having word-initial stop consonants with either English- or Spanish-appropriate voice onset times. Participants fixated interlingual distractors(nontarget pictures whose English names shared a phonological similarity with the Spanish targets) more frequently than control distractors when the target words contained English-appropriate voice onset times. These results demonstrate that fine-grained acoustic-phonetic information and a precise match between input and representation are criticalfor parallel activation of two languages.     

Kinetic study of hydrogen-induced direct phase transformation in Y2Fe17 magnetic alloy on the basis of Kolmogorov’s model

The kinetics of the hydrogen induced direct phase transformation in Y₂Fe₁₇ magnetic alloy has been analysed within the framework of Kolmogorov’s kinetic model. It is established that the transformation can be classified as a diffusion-controlled transformation, which occurs by a mechanism of nucleation and growth with a decreasing nucleation rate of new phases, namely α-Fe and YH₂. A kinetic equation has been obtained that well describes the isothermal kinetic curves of the phase transformation in Y₂Fe₁₇ as a function of the transformation temperature.     

After-effects induced by interactions between hydrogen and the martensite transformation in Ni–Ti superelastic alloy

The effects of dynamic interactions between hydrogen and a stress-induced martensite transformation on the recovery of deteriorated tensile properties by ageing in air at room temperature have been investigated for a Ni–Ti superelastic alloy. A specimen is subjected to single stress-induced martensite and reverse transformations immediately after hydrogen charging. Upon tensile testing, brittle fracture occurs in the latter half of the elastic deformation region of the martensite phase after the stress-induced martensite transformation. Upon ageing before the tensile test, fracture occurs during the stress-induced martensite transformation. In addition, the nano- and micro-morphologies of the brittle outer part of the fracture surface of the specimen are changed by ageing. Thus, the tensile properties markedly deteriorate, rather than recover, by ageing. The present results clearly indicate that dynamic interactions between hydrogen and the stress-induced martensite transformation have serious after-effects on hydrogen embrittlement of Ni–Ti superelastic alloy.     

Strain rate response of a Ni–Ti shape memory alloy after hydrogen charging

In this work, we investigate the susceptibility of Ni–Ti superelastic wires to the strain rates during tensile testing after hydrogen charging. Cathodic hydrogen charging is performed at a current density of 10?A/m² during 2–12?h in 0.9% NaCl solution and aged for 24?h at room temperature. Specimens underwent one cycle of loading-unloading reaching a stress value of 700 MPa. During loading, strain rates from 10^?6 to 5?×?10^?2?^?s^?1 have been achieved. After 8?h of hydrogen charging, an embrittlement has been detected in the tensile strain rate range of 10^?6 to 10^?4?s^?1. In contrast, no embrittlement has been detected for strain rates of 10^?3?s^?1 and higher. However, after 12?h of hydrogen charging and 24?h of annealing at room temperature, the embrittlement occurs in the beginning of the austenite-martensite transformation for all the studied strain rate values. These results show that for a range of critical amounts of diffused hydrogen, the embrittlement of the Ni–Ti superelastic alloy strongly depends on the strain rate during the tensile test. Moreover, it has been shown that this embrittlement occurs for low values of strain rates rather than the higher ones. This behaviour is attributed to the interaction between the diffused hydrogen and growth of the martensitic domain.     

Formation and hydrogen adsorption properties of Ti-Hf-Ni quasicrystals and crystal approximants

The formation of a high-order rational approximant (RA) phase in rapidly quenched Ti-Hf-Ni alloys and the hydrogen absorption properties of that phase are reported. Electron diffraction patterns show systematic shifts of the diffraction spots from their expected positions for the icosahedral phase (i-phase); the diffraction patterns are consistent with those expected for a 3/2 RA phase RA-(Ti-Hf-Ni). Based on differential scanning calorimetry studies, RA-(Ti-Hf-Ni) is metastable, transforming between 350 and 500°C to a quasicrystal with strong phason disorder. This crystallizes at 620°C to a Ti 2 Nitype phase. RA-(Ti-Hf-Ni) readily absorbs hydrogen, up to 1.2 hydrogen atoms per metal atom ([H][M] =1.2). Pressure-composition isotherm studies for gasphase loading show that the pressure plateau for RA-(Ti-Hf-Ni) is similar to that observed for the i-(Ti-Zr-Ni) phase, although it occurs at as lightly higher pressure and extends over a smaller range of hydrogen concentrations. Unlike i-(Ti-Zr-Ni), no irreversible hydride phase forms with hydrogen loading at 250°C, suggesting that RA-(Ti-Hf-Ni) may have superior cycling properties, of interest for hydrogen storage applications.     

Robustness to temporal constraint explains expertise in ball-over-net sports

The present study investigated motor expertise in interpersonal competitive ball-over-net sports in terms of a dynamical system with temporal input. In a theoretical framework, the behavior of the system is characterized by a fractal-like structure according to switching input, which changes uniquely according to the duration of input and internal parameter of the system. We investigated periodic movements, in which the player executed a forehand or backhand stroke repeatedly, and continuous switching movements, in which the player continuously switched between two movement patterns corresponding to hitting the ball under two ball directions and with six temporal constraint conditions during a table tennis rally. In the periodic movement, we observed two limit-cycle attractors corresponding to each direction in the phase space independent of temporal constraint or skill level. Conversely, in the continuous switching movement, a transition in trajectories between the two limit-cycle attractors was observed in the phase space, and this transition was characterized by a fractal-like structure. The fractal-like structure moved closer to the random structure as temporal constraint increased independent of skill level. However, the temporal constraint condition closest to the random structure was higher for the advanced players than for the novices, indicating that robustness to the temporal constraint was higher for the advanced players than for the novices. Our results suggest that motor expertise in interpersonal competitive ball-over-net sports is more robust to temporal constraints with various inputs.     

How a high working memory capacity can increase proactive interference

Previous findings suggested that a high working memory capacity (WMC) is potentially associated with a higher susceptibility to proactive interference (PI) if the latter is measured under high cognitive load. To explain such a finding, we propose to consider susceptibility to PI as a net effect of individual executive processes and the intrinsic potential for PI. With the latter, we refer to the amount of information that is activated at a given time and that has the potential to exert PI subsequently. In two studies deploying generalized linear mixed models, susceptibility to PI was modeled as the decline of performance over trials of a complex span task. The results revealed that a higher WMC was associated with a higher susceptibility to PI. Moreover, the number of stimuli recalled in one trial as a proxy variable for the intrinsic potential for PI negatively affected memory performance in the subsequent trial.     

Structure of a phase induced with Xe-ion irradiation-implantation in γ-TiAl

A phase transformation in γ-TiAl intermetallic alloy was found to be induced with 50keV Xe-ion irradiation-implantation at doses larger than 2.2 x 10¹⁸ ions m^-2 at room temperature. The structure and the chemical composition of the induced phase were investigated with high-resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy. The zones of the induced phase have sizes up to about several tens of nanometres. The phase has a hexagonal structure with a = 0.286 nm and c = 0.462nm. The crystallographic orientation relationship between the phase (P) and the gamma-TiAl matrix is (001)_P//(111)_γ and \[100]_P//[011]_γ. The \[Al]/[Ti] atomic composition ratio in the phase is analysed to be 56/44, slightly different from that of the matrix, 51/49. These results suggest that the induced phase is an Al solid solution of α-Ti alloy phase, which has different structural parameters and chemical composition from those of the reported phase. It is suggested that the size of the ions is important in the phase transformation.     

Monitoring of learning for emotional faces: how do fine-grained categories of emotion influence participants’ judgments of learning and beliefs about memory?

Researchers have evaluated how broad categories of emotion (i.e. positive and negative) influence judgments of learning (JOLs) relative to neutral items. Specifically, JOLs are typically higher for emotional relative to neutral items. The novel goal of the present research was to evaluate JOLs for fine-grained categories of emotion. Participants studied faces with afraid, angry, sad, or neutral expressions (Experiment 1) and with afraid, angry, or sad expressions (Experiment 2). Participants identified the expressed emotion, made a JOL for each, and completed a recognition test. JOLs were higher for the emotional relative to neutral expressions. However, JOLs were insensitive to the categories of negative emotion. Using a survey design in Experiment 3, participants demonstrated idiosyncratic beliefs about emotion. Some people believed the fine-grained emotions were equally memorable, whereas others believed a specific emotion (e.g. anger) was most memorable. Thus, beliefs about emotion are nuanced, which has important implications for JOL theory.     

Input- and output-monitoring in implicit and explicit memory

Previous experiments have shown that the procedure of questioning subjects retrospectively about the input and output status of information (input and output monitoring) is a useful method for assessing the awareness states of subjects during implicit and explicit memory tasks. The main purpose of the present study was to investigate whether the previous findings could be extended to other implicit and explicit memory tasks. We were especially interested in whether differences in input- and output-monitoring performance can be observed when both the implicit and explicit memory tasks are conceptual ones. In a final test phase, the target items from the study phase and new distractor items were presented. In a recognition-like situation, subjects had to decide whether an item had been presented in the study phase (input status), as well as whether they had produced the item in the memory-test phase (output status). In all three experiments judgments about the input status - but only for those items that had been produced in the implicit or in the explicit memory test - were more precise after explicit than after implicit memory testings. This finding was not influenced by the distinction between perceptual and conceptual-memory tasks (Exp. 1), and was obtained under conditions in which the implicit and the explicit memory tasks were both conceptual and differed only in test instructions (Exps. 2 and 3). These results suggest that not only subjects performing a perceptual test of implicit memory, but also subjects in a conceptual implicit test were less aware of using information from a previous study episode than subjects who received memory instructions. It is concluded that requiring judgments about the input status of information is a good method for assessing subjects test awareness and is preferable to the use of a questionnaire (Exp. 3). In contrast, in all three experiments no differences were found with the output-monitoring measure between implicit and explicit test conditions.     

Hydrogen-assisted damage in austenite/martensite dual-phase steel

For understanding the underlying hydrogen embrittlement mechanism in transformation-induced plasticity steels, the process of damage evolution in a model austenite/martensite dual-phase microstructure following hydrogenation was investigated through multi-scale electron channelling contrast imaging and in situ optical microscopy. Localized diffusible hydrogen in martensite causes cracking through two mechanisms: (1) interaction between {1?1?0}_M localized slip and {1?1?2}_M twin and (2) cracking of martensite–martensite grain interfaces. The former resulted in nanovoids along the {1?1?2}_M twin. The coalescence of the nanovoids generated plate-like microvoids. The latter caused shear localization on the specific plane where the crack along the martensite/martensite boundary exists, which led to additional martensite/martensite boundary cracking.     

Social anxiety and cognitive expectancy of aversive outcome in avoidance conditioning

Fear conditioning studies have shown that social anxiety is associated with enhanced expectancy of aversive outcome. However, the relation between cognitive expectancy and social anxiety has never been tested in avoidance conditioning paradigms. We compared 48 low (LSA) and high socially anxious individuals (HSA) on subjective expectancy of aversive outcome during an avoidance conditioning task. Displays of neutral faces were coupled with an aversive outcome (US): a shout and a shock. Participants could avoid the US by pressing a correct button from a button box. First, HSA showed higher US expectancy than LSA during the initial phase of avoidance conditioning, supporting the view that socially anxious individuals have an expectancy bias when social situations are ambiguous. Second, when the avoidance response became unavailable, LSA showed lower US expectancy than HSA, suggesting that low socially anxious individuals are prone to a positive bias when perceived threat is high. A lack of such positive bias in socially anxious individuals may lead to higher susceptibility to safety behavior interpretations. Together, these findings support the role of cognitive processes in avoidance conditioning and underscore the relevance to encounter avoidance learning when studying social anxiety.     

Dynamic precipitation at elevated temperatures in a dual-phase AlCoCrFeNi high-entropy alloy: an in situ study

ABSTRACT

The effect of a possible phase transformation or precipitation of the face-centred cubic (FCC) phase on intermediate-temperature deformation of a dual-phase AlCoCrFeNi high-entropy alloy has been studied using in situ tensile testing at 550°C. Electron backscatter diffraction (EBSD) results showed localised precipitation of the FCC phase during the intermediate-temperature deformation. The overall fracture behaviour and crack propagation of the material was not altered much compared to the room-temperature behaviour, namely brittle trans-granular fracture. Deformation at higher temperatures (above 750°C) is suggested as a way to enhance the dynamic FCC phase precipitation, in order to improve the ductility or deformability of the alloy.     

Aging and input processing in dual-task situations

The psychological refractory period (PRP) paradigm was used to test whether older participants suffer from input interference in dual-task situations. Young (24 years) and older (57 years) adults gave speeded responses to 2 successively presented stimuli. The results showed increased susceptibility of older participants to input interference. Further experiments revealed that this input interference is related to the salience of the 2nd stimulus and that it is specific to older participants. Our findings indicate that parallel processing at the input stages of dual-task performance requires cognitive control. An age-related decline in the control of input processes should be considered as one source of age effects in dual-task performance.     

Psychosocial correlates of condom use and their relationship with worry about STI and HIV in native and immigrant adolescents in Spain

The goal of this study was to analyze how worry about sexually-transmitted infections (STI) and HIV influences attitudes and self-efficacy towards condom use, HIV-related knowledge, HIV-perceived susceptibility and HIV-misconceptions in a multicultural sample in Spain. The sample was composed of 3,051 adolescents aged between 14 and 19 years old who lived in Spain. Of these, 67.7% were native Spaniards and the remaining 32.3% were Latin American immigrants. Results showed that worry about STI and HIV has a direct influence on condom use self-efficacy and HIV-knowledge and HIV-perceived susceptibility. Native Spanish adolescents showed higher positive attitudes towards condom use, greater HIV-knowledge and HIV-perceived susceptibility, and lower negative attitudes towards condoms use and HIV-misconceptions than Latin American adolescents. In the discussion, the importance of worry about STI and HIV is highlighted as a mediator variable that can predict risky sexual behavior and is related to cultural origin.     

Tests of the generality of the principle of encoding specificity

Two empirical tests of the principle of encoding specificity are reported. In Experiment I, the normative strength of the cues presented on the input and on the recall trial was varied factorially. To lessen the emphasis on strictly associative learning, only half the items were cued in each phase of the study-recall cycle. Recall was higher when the cues remained the same than when they changed. However, regardless of the condition of input cuing, strong output cues were substantially more effective than weak ones. In Experiment II, the to-be-remembered words were shown in the presence of weak cues on the input trial. Recognition in the context of strong extralist cues was compared with recall to the original input cues. On the test of cued recognition, the target words were either generated by the subjects as free associates or presented to them as items on a test constructed by the experimenter. Contrary to previous findings, recall was not found to be superior to recognition. The phenomena of cue-dependent forgetting that have been interpreted as evidence for the principle of encoding specificity appear to have limited generality.     

Synthesis of amorphous and quasicrystal phases by mechanical alloying of Ti 45 Zr 38 Ni 17 powder mixtures,and their hydrogenation

Mechanical alloying of Ti 45 Zr 38 Ni 17 powder mixture forms an amorphous phase, but subsequent annealing causes the formation of an icosahedral ( i ) phase. The maximum hydrogen concentration that can be loaded at 573K at a hydrogen pressure of 3.8MPa is the same (\[H]/\[M] 1.5) for the amorphous and i -phase powders. With hydrogenation, the i -phase is almost stable, forming no hydrides, whereas the amorphous phase transforms to a fcc hydride. The activation energy for hydrogen desorption for the i -phase is about 127kJmol -1, which is lower than that for the amorphous phase, suggesting that the i -phase powder may have better properties for hydrogen-storage applications.