Origin of lattice strain in nanocrystalline materials

A striking feature of nanocrystalline (NC) materials prepared by different techniques is the variation of lattice strain present in the crystallites. A simple model is proposed to account for this phenomenon, which allows the establishment of a quantitative relationship describing the dependence of the crystal lattice strain on the grain size. Good agreement between theoretical and experimental data indicates that the stress field, induced by the excess volume in grain boundaries, is the dominant source of the lattice strain.     

Mechanical-milling-induced amorphization of Se: A crystallite destabilization model

Complete solid-state amorphization has been realized in elemental Se by means of mechanical milling of crystalline Se powder. Quantitative X-ray diffraction and thermal analyses were employed to characterize the amorphization process and indicated that the amorphization onset corresponds to a critical crystallite size and a drop in microstrain. During the major amorphization process, the remaining crystallite size remains unchanged with a constant lattice expansion. A new kinetics model of crystallite destabilization is proposed for the solid-state amorphization which satisfactorily explains the experimental observations.     

On the persuadability of memory: Is changing people's memories no more than changing their minds?

The observation of parallels between the memory distortion and persuasion literatures leads, quite logically, to the appealing notion that people can be ‘persuaded’ to change their memories. Indeed, numerous studies show that memory can be influenced and distorted by a variety of persuasive tactics, and the theoretical accounts commonly used by researchers to explain episodic and autobiographical memory distortion phenomena can generally predict and explain these persuasion effects. Yet, despite these empirical and theoretical overlaps, explicit reference to persuasion and attitude‐change research in the memory distortion literature is surprisingly rare. In this paper, we argue that stronger theoretical foundations are needed to draw the memory distortion and persuasion literatures together in a productive direction. We reason that theoretical approaches to remembering that distinguish (false) beliefs in the occurrence of events from (false) memories of those events – compatible with a source monitoring approach – would be beneficial to this end. Such approaches, we argue, would provide a stronger platform to use persuasion findings to enhance the psychological understanding of memory distortion.     

Do Phonological Constraints on the Spoken Word Affect Visual Lexical Decision?

Reading a word may involve the spoken language in two ways: in the conversion of letters to phonemes according to the conventions of the language’s writing system and the assimilation of phonemes according to the language’s constraints on speaking. If so, then words that require assimilation when uttered would require a change in the phonemes produced by grapheme-phoneme conversion when read. In two experiments, each involving 40 fluent readers, we compared visual lexical decision on Korean orthographic forms that would require such a change (C stimuli) or not (NC stimuli). We found that NC words were accepted faster than C words, and C nonwords were rejected faster than NC nonwords. The results suggest that phoneme-to-phoneme transformations involved in uttering a word may also be involved in visually identifying the word.     

Atom vacancies at a screw dislocation core in SrTiO3

A screw dislocation in strontium titanate has been studied taking benefit of negative spherical aberration-imaging in a spherical aberration-corrected transmission electron microscope. The core structure of the dislocation is atomically resolved with respect to both cation and oxygen columns by the inclusion of the central core area. The dislocation core is characterized by a helical distortion of the lattice planes, which leads, in particular, to azimuthally elongated image dots associated with individual atomic columns close to the core centre. The atomic coordination in the dislocation core is identified and a high density of atom vacancies is revealed for a Ti–O column at the core.     

Testing curvatures of learning functions on individual trial and block average data

Many models offer different explanations of learning processes, some of them predicting equal learning rates between conditions. The simplest method by which to assess this equality is to evaluate the curvature parameter for each condition, followed by a statistical test. However, this approach is highly dependent on the fitting procedure, which may come with built-in biases difficult to identify. Averaging the data per block of training would help reduce the noise present in the trial data, but averaging introduces a severe distortion on the curve, which can no longer be fitted by the original function. In this article, we first demonstrate what is the distortion resulting from block averaging. Theblock average learning function, once known, can be used to extract parameters when the performance is averaged over blocks or sessions. The use of averages eliminates an important part of the noise present in the data and allows good recovery of the learning curve parameters. Equality of curvatures can be tested with a test of linear hypothesis. This method can be performed on trial data or block average data, but it is more powerful with block average data.     

Assessing change with the extended logistic model

The purpose of this article is to define a method for the assessment of change. A reinterpretation of the extended logistic model is proposed. The extended logistic model for the assessment of change (ELMAC) allows the definition of a time parameter which is supposed to identify whether change occurs during a period of time, given a specific event or phenomenon. The assessment of a trend of change through time, on the basis of the time parameter which is estimated at different successive occasions during a period of time, is also considered. In addition, a dispersion parameter is calculated which identifies whether change is consistent at each time point. The issue of independence is taken into account both in relation to the time parameter and the dispersion parameter. An application of the ELMAC in a learning process is presented. The interpretation of the model parameters and the model fit statistics is consistent with expectations.     

Tactile perception of thermal diffusivity

The thermal diffusivity of an object is a parameter that controls the rate at which heat is extracted from the hand when it touches that object. It is an important feature for distinguishing materials by means of touch. In order to quantitatively describe the ability of human observers to discriminate between materials on the basis of heat extraction rate, we conducted an experiment in which this heat extraction was performed in a controlled way. In different conditions, subjects were repeatedly asked to select from two stimuli the one that cooled faster. The discrimination threshold was around 43% of the extraction rate. A rate that was twice as slow also yielded twice the absolute threshold. When we halved the temperature difference between the beginning and end of the stimulus, the threshold did not change as much. In separate experiments, we investigated the different cues that were available in the stimulus: initial cooling rate and end temperature. Both cues were used for discrimination, but cooling rate seemed to be the most important.     

Icosahedral quasicrystal in annealed ZnMgSc alloys

A new icosahedral quasicrystal has been found in Zn 85-x Mg x Sc 15 ( x = 3,4,5) alloys annealed at 922K for 5-100h. Electron diffraction and powder X-ray diffraction experiments indicate that this quasicrystal has a primitive icosahedral quasilattice (P type) and a six-dimensional lattice parameter a 6D =0.7115nm. The stoichiometric composition of the icosahedral quasicrystal was estimated to be close to Zn 80 Mg 5 Sc 15, since the icosahedral quasicrystal coexists in the x = 5 samples with small amounts of a MgZn 2 -type Laves phase and a Zn 17 Sc 3 -type cubic phase with lattice parameter a =1.3854nm. The latter is interpreted to be a 1/1-type approximant crystal of the icosahedral quasicrystal. The atomic cluster included in the Zn 17 Sc 3 -type cubic phase indicates a structural similarity between the Zn-Mg-Sc quasicrystal and the Cd-Yb (and Cd-Ca) icosahedral quasicrystals recently reported.     

Construction of Smoking-Relevant Risk Perceptions Among College Students: The Influence of Need for Cognition and Message Content1

Changing smokers' health-risk perceptions has been difficult. This study tested whether need for cognition (NC)—a factor within Petty & Cacioppo's (1986) elaboration likelihood model that reflects the preference for effortful cognitive information processing—moderated responses to a smoking risk message intervention. College smokers (n=227) evaluated a fact-based or emotion-based smoking risk pamphlet or a control pamphlet. Among occasional but not daily smokers, NC interacted as hypothesized with type of message to moderate risk perceptions. Among participants with higher NC, the fact-based message produced the greatest increase in risk perception; whereas among participants with lower NC, the emotion-based message produced the greatest change. Findings demonstrate that individual differences in cognitive processing can influence the potency of health-risk messages.     

Gait symmetric adaptation: Comparing effects of implicit visual distortion versus split-belt treadmill on aftereffects of adapted step length symmetry

Understanding gait adaptation is essential for rehabilitation, and visual feedback can be used during gait rehabilitation to develop effective gait training. We have previously shown that subjects can adapt spatial aspects of walking to an implicitly imposed distortion of visual feedback of step length. To further investigate the storage benefit of an implicit process engaged in visual feedback distortion, we compared the robustness of aftereffects acquired by visual feedback distortion, versus split-belt treadmill walking. For the visual distortion trial, we implicitly distorted the visual representation of subjects’ gait symmetry, whereas for the split-belt trial, the speed ratio of the two belts was gradually adjusted without visual feedback. After adaptation, the visual feedback or the split-belt perturbation was removed while subjects continued walking, and aftereffects of preserved asymmetric pattern were assessed. We found that subjects trained with visual distortion trial retained aftereffects longest. In response to the larger speed ratio of split-belt walking, the subjects showed an increase in the size of aftereffects compared to the smaller speed ratio, but it steeply decreased over time in all the speed ratios tested. In contrast, the visual distortion group showed much slower decreasing rate of aftereffects, which was evidence of longer storage of an adapted gait pattern. Visual distortion adaptation may involve the interaction and integration of the change in motor strategy and implicit process in sensorimotor adaptation. Although it should be clarified more clearly through further studies, the findings of this study suggest that gait control employs distinct adaptive processes during the visual distortion and split-belt walking and also the level of reliance of an implicit process may be greater in the visual distortion adaptation than the split-belt walking adaptation.     

Ab initio investigation of electron-phonon interaction in LaSn3 and CaSn3

ABSTRACT

We present results for the structural, electronic, vibrational, and electron-phonon coupling properties of LaSn₃ and CaSn₃ adopting the simple cubic AuCu₃-type structure obtained using the the generalised gradient approximation of the density functional theory and plane wave ab initio pseudopotential method. Our electronic results show that both materials display metallic character with several bands, which have mainly Sn 5p character, crossing the Fermi level. The calculated phonon spectrum of LaSn₃ accords very well with reported experimental measurements. The weights of the peaks in the Eliashberg spectral function of both compounds are enhanced with the use of experimental lattice constant in our electron-phonon calculation, increasing the value of average electron phonon coupling parameter from 0.876 to 0.937 for LaSn₃ (by 7%) and from 0.642 to 0.725 for CaSn₃ (by 13%). The use of experimental lattice constant also improves the agreement between theoretical and experimental values of the superconducting temperature for both compounds.     

Quasi-two-dimensional or hcp palladium nanoparticles with host-guest interaction prepared at room temperature

Quasi-two-dimensional palladium nanoparticles with an average lateral dimension of 7 nm have been prepared by reduction of a PdCl₂ graphite intercalation compound precursor by lithium-diphenylide in tetrahydrofuran at room temperature. Selected-area electron diffraction patterns provide evidence that the palladium nanoparticles are hcp single-crystal particles. Owing to the template effect of the graphite lattice, the lattice parameter of palladium was found to have a strong relation with the graphite, and a 3a _graphite superstructure was inferred. The palladium structure is rotated by 30^o with regard to the carbon host lattice. Raman spectroscopy on this sample showed that a charge transfer between carbon and palladium occurs. The sample can be considered as a common Pd-graphite intercalation compound with palladium nanoparticles as guest. This behaviour is different from palladium nanoparticles prepared by hydrogen reduction at higher temperatures from the same precursor material. These particles may represent an early stage of nanoparticle formation.     

A timing-specific memory distortion effect in young children

It has been suggested that there are systematic distortions in children's memory for temporal durations, such that children's memory is not just less accurate than that of adults but qualitatively different. Experiment 1 replicated the memory distortion effect by demonstrating developmental change in the tendency to confuse a reference duration with one that is shorter rather than longer than it. When the long-term memory demands of the task were reduced by providing reminders of the reference duration on every trial, there were no such qualitative changes in error patterns (Experiment 2). Further evidence for developmental changes in memory distortion was found in the temporal generalization task of Experiment 3, in which stimuli were spaced logarithmically rather than linearly. In Experiment 4, a similar distortion pattern was absent in a task in which children made judgments about the pitch rather than the duration of stimuli, suggesting the effect may be specific to time estimation.     

Mechanical hysteresis due to microplasticity in alumina with microcracks

Abstract

Stress-strain hysteresis in alumina with microcracks has been investigated by a loading–unloading test in the microstrain range around 10 ^?4 While there remains a permanent strain after the initial loading, steady-state cyclic loading results in a single closed hysteresis loop with a symmetrical shape. Such a stabilized hysteresis loop is responsible for internal friction and can be attributed to the microplasticity associated with a forerunning phenomenon of fracture.     

Memory distortion and attitude change—Two routes to cognitive balance

We report novel research investigating memory distortion as an alternative route to cognitive balance, comparing it with attitude change as a well‐known balancing mechanism. Participants received statements from multiple communicators about a controversial topic (national pride in Study 1 and climate protection in Study 2) and remembered these statements immediately or 1 week later. This resulted in initially balanced or unbalanced combinations of the liking for individual communicators and the communicators' statements and in subsequent balance increases due to liking change or misremembering of statements. The contribution of memory distortion to balance was significant but weaker and less efficient than that of liking change, and the contributions were empirically independent (i.e., uncorrelated and differentially related to third variables—specifically, memory strength and individual cognitive consistency motivation). They also had a different temporal trajectory (liking change fast and memory distortion slow). We discuss theoretical and practical implications.     

Shear-driven damage of ductile metals induced by indentation load

Although indentation does not induce apparent cracking in ductile materials, degradation of elastic stiffness of ductile metals has been found in micro-/macro- indentation tests. After comparing the predicted degradation by extended damaged-plasticity models with that measured by experimental testing, it is found that the softening caused by distortion of existing voids is inadequate to cause the notable degradation of elasticity. It is suggested that an independent damage-nucleation mechanism arising from shear deformation may exist. Although attractive in practical applications for its non-destructive nature, the damage-based indentation technique for estimating the fracture properties of ductile materials needs further investigation.     

Twinning in the structure of the ‘decagonal’ phase Al65Cu20Co15

Abstract

The existence of twinning in the pseudo-decagonal phase Al₆₅Cu₂₀Co₁₅ has been established through TEM studies. From electron diffraction patterns, a rhombic crystalline lattice with a very large unit cell is easily identified. Diffraction patterns for microtwinned regions exhibit splitting and distortion of the reflections which is a result of the overlap of lattices which are rotated by 36° with respect to one another. While patterns from single components of the twins exhibit only pseudo-tenfold symmetry, those from the microtwinned regions exhibit nearly perfect tenfold symmetry.     

Visual perception of thick transparent materials

Under typical viewing conditions, human observers readily distinguish between materials such as silk, marmalade, or granite, an achievement of the visual system that is poorly understood. Recognizing transparent materials is especially challenging. Previous work on the perception of transparency has focused on objects composed of flat, infinitely thin filters. In the experiments reported here, we considered thick transparent objects, such as ice cubes, which are irregular in shape and can vary in refractive index. An important part of the visual evidence signaling the presence of such objects is distortions in the perceived shape of other objects in the scene. We propose a new class of visual cues derived from the distortion field induced by thick transparent objects, and we provide experimental evidence that cues arising from the distortion field predict both the successes and the failures of human perception in judging refractive indices.     

Sedimentation of substitutional atoms and phase change in an In-Pb alloy under an ultrastrong gravitational field

It was found that an atomic-scale graded structure was formed, and a phase change occurred, in an In–Pb alloy by the sedimentation of substitutional solute atoms under an ultrastrong gravitational field (820?000?g (maximum); 150°C; 100?h). Continuous gradients in the concentration of Pb (from about 6 to 45?at.%) and In (from about 94 to 55?at.%) and resulting changes in the lattice constant were observed. Fcc (Pb-rich) and tetragonal (In-rich) phases appeared in the strong- and weak-gravity regions respectively from a single starting fct α phase. It is suggested that sedimentation of substitutional atoms can be used to control the compositions and structure of bulk materials and also thin films or layer interfaces.