Twinning of quasicrystals and related structures

Abstract

We consider for the first time twinning in quasicrystals and related structures in a systematic manner. The twinning operations are considered in the framework of six-dimensional crystallography. The number of twin variants and the symmetry of twinned aggregates are also discussed. It is shown that essentially two different types of interface can arise between any two twin variants.     

A space to “eat,trance, and sleep”: the healing power of Mahanubhav temples in Maharashtra (India)

This paper explores the effectiveness of religious healing by focusing on one important factor that has been much neglected – the stay within the shrine. Drawing on qualitative research in Mahanubhav temples in India, this paper emphasises that the central part of religious healing is the process of being in the temple and becoming familiar with shrine culture. At the same time, I argue that the social space of the shrine is important not only for the benefits of a soothing environment or support system. It is argued that temporary residence within the shrine enables individuals to develop long-term associations with the religious community and sect. Through discussion of indicative cases, this paper elaborates on the process of “becoming a Mahanubhav pilgrim” that is at the heart of temple healing practices in India.     

Frank's 'cubic' hexagonal phase: An intermetallic cluster compound as an example

Frank introduced in 1965 the novel idea of projection from a four-dimensional cube to recover the points of a hexagonal lattice with a special c / a ratio of ( 3 - 2 ½. This was called a cubic hexagonal crystal, as there was a similarity to the conventional cubic crystals in that directions were perpendicular to planes with the same Miller-Bravais indices. While a number of crystals in the NiAs-Ni 2 In family have been reported with this special axial ratio, the number of atoms in the unit cell is small. As the first example of an intermetallic cluster compound, we identify µ-Al 4 Mn, µ-Al 4 Cr, Zn-Mg-Sm and a host of related intermetallics featuring a special aggregate of icosahedra as Frank's 'cubic' hexagonal phase or its variant. The metric is generated by the Friauf polyhedra and the icosahedral linkages and leads to a multimetric crystal and several interesting connections with hexagonal quasicrystals, hexagonal phases and derivative orthorhombic and lower-symmetry structures.     

Electron diffraction patterns from the Al–Mn decagonal phase

Abstract

The variety of electron diffraction patterns arising from the decagonal phase has been explored using a stereographic analysis for generating the important zone axes as intersection points corresponding to important relvectors. An indexing scheme employing a set of five vectors and an orthogonal vector has been followed. A systematic tilting from the decagonal axis to one of the twofold axes has been adopted to generate a set of experimental diffraction patterns corresponding to the expected patterns from the stereographic analysis with excellent agreement.     

On the short-range order in Al-Mn quasicrystals during low-temperature ageing

Abstract

We report the evolution of diffuse intensity during the low-temperature ageing of Al-Mn quasicrystals. This is taken as evidence of short-range order in the icosahedral phase prior to its decomposition. The implication of these diffuse intensities is discussed     

Online feedback and the regulation of degrees of freedom in motor control

We tested the hypothesis that the degree to which online feedback is used to control movement influences the regulation of degrees of freedom in a task. Ten participants performed an isometric force production task with their two index fingers with the goal of matching the total force to a target waveform. The role of online feedback was manipulated by changing three factors - the tracking mode, the profile of the target waveform, and the visual gain. The results showed that the coupling between the finger forces was lower in conditions where participants used online feedback to correct their movements compared to conditions where more feedforward strategies were used. The availability of online feedback is dependent on the nature of the task and this contributes to task-dependent changes in the regulation of the degrees of freedom.     

Evolution of superlattice order in Al–Mn quasicrystals and its relation to face-centred icosahedral quasicrystals

Abstract

We have established a simple icosahedral to face-centred icosahedral ordering transformation in Al–Mn quasicrystals. This result strongly supports the view that the recently discovered face-centred icosahedral quasicrystal in ternary Al–Cu–Fe and related alloys represents a long-range superstructure of simple icosahedral quasicrystals     

Asian-Indian Parents’ Attributions About the Causes of Child Behavior: A Replication and Extension With Parents From Chennai,India

Using hypothetical vignettes, 152 parents of children 10–17 years old living in Chennai, India, made attributions about whether the origins of 2 positive and 2 negative behaviors performed by their own child or another child were due to the child's personality or the situation, or to parenting or nonparenting influences based on the frequency, intensity, and cross-situational consistency of the behavior. Parents attributed the positive behaviors of all children to the personality of the child and to parenting. Parents attributed negative behavior of their own children to situational influences and nonparenting effects, but attributed the negative behavior of other children to their personality and to parenting, a pattern that enhances and reinforces parent self-esteem. Results were discussed in terms of the self-serving bias and the actor–observer bias, cognitive distortions that protect and enhance parents’ views of themselves and their children.     

Motor Learning through Induced Variability at the Task Goal and Execution Redundancy Levels

The authors examined the influence of introducing variability at two different levels in the learning of a striking task. Variability at the task goal level was introduced by changing target location, whereas variability at the execution redundancy level was introduced by using an intermediate target that constrained participants to use different paths from trial to trial to strike the same target. After practice, participants were transferred to 2 test conditions: (a) a fixed-target test, where the position of the target was unchanged; and (b) a variable-target test, where the position of the target was varied from trial to trial. The results from the manipulation at the task goal level were consistent with predictions from the specificity of practice hypothesis. In both the fixed- and variable-target tests, the best performance was achieved by the group that had practiced in the condition matching the test condition. At the execution-redundancy level, practicing multiple solutions to achieve the task goal did not improve performance in either the fixed- or variable-target tests. These results show that introducing variability at the task goal and execution redundancy levels has different effects on learning and generalization and that practice schedules that constrain the participant to use redundant solutions may not facilitate learning.