Structures of Ti2(Ni,V) in crystalline and quasicrystalline phases

Abstract

A new criterion for the classification of quasicrystalline structures is proposed. A quasicrystal with composition close to a Frank-Kasper phase, which consists exclusively of tetrahedra, should belong to the i((Al, Zn)₄₉Mg₃₂) class whereas one with composition close to that of the crystal, which consists of both tetrahedra and octahedra, should belong to the i(A1MnSi) class. The Ti₂(Ni, V) building block consists of four icosahedra and a truncated tetrahedron. Replacing the eight carbon atoms of a diamond unit cell with this building block produces the Ti₂(Ni, V) crystal. Placing a distorted Ti₂(Ni, V) building block on a threefold axis of an icosahedrally symmetric point group and operating on it by this point group gives a double Mackay icosahedron. It can be concluded that the Ti₂(Ni, V) and α-AlMnSi quasicrystals are isomorphic structures since Ti₂(Ni, V) and α-A1MnSi crystals consist of both tetrahedra and octahedra.     

Synthesis of nanostructured vanadium powder by high-energy ball milling: X-ray diffraction and high-resolution electron microscopy characterization

Vanadium metal powders, ball milled with different surfactants viz., stearic acid, KCl and NaCl, have been studied by X-ray diffraction and transmission electron microscopy. The surfactants alter the microstructural and morphological characteristics of the powders. Ball milling with stearic acid results in solid-state amorphization, while powders milled with KCl yield vanadium–tungsten carbide nanocomposite mixtures. NaCl proved to be an excellent surfactant for obtaining nanostructured fusion-grade vanadium powders. In order to understand the reaction mechanism behind any interstitial addition in the ball-milled powders, CHNOS analysis was performed.     

Transformation of the decagonal quasicrystalline phase to a B2 crystalline phase in the Al-Cu-Co system by high-energy ball milling

Samples of a decagonal quasicrystalline phase, located in the Al-Cu-Co system and synthesized by a slow cooling technique, have been mechanically milled in a high-energy planetary ball mill for 10, 20 and 30h. The milled powders, as well as powders that had been annealed (after milling) for times ranging from 30 to 150min at 600C, were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. A phase transformation from the decagonal phase to a B2 crystalline phase during highenergy ball milling is reported here for the first time. Powders milled for more than 10h contained predominantly the B2-type crystalline phase with a lattice parameter of 0.29nm. This crystalline phase was found to be quite stable after milling for 30h and also on subsequent annealing at 600C. These experimental results lend support to an earlier suggestion that the decagonal phase in Al-Cu-Co is actually less stable than the B2 phase at low temperatures.     

Measurement of the relative strain ratios normal to the crystal planes in Cu thin films using grazing incidence X-ray diffraction

The relative strain normal to the crystal planes in Cu thin films has been experimentally measured using grazing incidence X-ray diffraction. This was performed by measuring the ratio of the strain exerted in the same specific (hkl) crystal plane parallel and perpendicular to the film surface. The strain ratios of the (1?1?1), (2?0?0), (2?2?0) and (3?0?0) planes were found to be –0.804, –1.324, –1.003, and –1.369, respectively. These values are within experimental error of those calculated theoretically under the assumptions of plane stress conditions.     

Neutron and X-ray diffraction studies and cohesive interface model of the fatigue crack deformation behavior

The crack-tip deformation behavior during a single overload, fatigue test of ferritic stainless steel, and Ni-based HAYNES 230 superalloy is studied at different structural levels using (1) neutron-diffraction, from which both the elastic-lattice strain and volume-averaged total dislocation densities are obtained, (2) polychromatic X-ray microdiffraction to probe the geometrically necessary dislocations and boundaries distribution, and (3) an irreversible and hysteretic cohesive interface model which has been implemented into a finite element framework to simulate the stress/strain evolution near the fatigue crack tip. Neutron strain measurements and finite element simulations are in qualitative agreement on the macroscopic length scale. Large plastic deformation induced by the overload and the resulting compressive residual strains are observed in front of the crack tip after the overload, and are the principal reason for the fatigue-crack-growth retardation. Strong strain gradients surrounding the crack propagation result in the formation of a high density of geometrically necessary dislocations near the fractured surface and cause local lattice rotations on the submicron level.     

New 1/1 cubic approximant phases in the Al-Cu-Ru-Si system studied by electron diffraction and high-resolution electron microscopy

Two types of new Al-Cu-Ru-Si 1/1 cubic approximant phases, both of which have cell parameters a=12.68A have been found in an as-cast Al_58.5Cu₁₈Ru_13.5Si₁₀ alloy. The two phases have sc and bcc structures respectively and are finely mixed in transmission electron microscopy observations. It is proposed that the sc structure is caused by ordering of atoms in the bcc structure.     

Comparison between Gudjonsson Suggestibility Scale 2 (GSS2) and Bonn Test of Statement Suggestibility (BTSS) in measuring children’s interrogative suggestibility

Susceptibility of children to leading questions and interrogative pressure is an important forensic issue. The most used techniques for assessing interrogative suggestibility are the Gudjonsson Suggestibility Scales (GSS) and the Bonn Test of Statement Suggestibility (BTSS). Apart from minor differences, the two tests, investigate the same dimensions: Yield, Shift, Immediate Recall, and Total Suggestibility. In this study, to investigate correlation measures for the corresponding variables in the two tests, we individually examined 84 children from the fourth and fifth grades (44 boys and 40 girls). All the participants completed the GSS2 the BTSS-1, the Vocabulary and the Similarity subtests of the WISC-R, and Raven’s Colored Progressive Matrices. No significant gender differences were observed for any of the variables studied. Comparison between the corresponding variables for the two tests showed a positive correlation. Yield and Total Suggestibility scores correlated negatively with the three cognitive variables. We conclude that although the two suggestibility scales measure analogous variables, the BTSS seems more suitable than the GSS2 for assessing a child’s suggestibility during police and forensic interviews.     

Modal Dispositionalism and the (T) Axiom

Philosophia - Yates has recently argued that modal dispositionalism invalidates the (T) axiom. Both Yates and Allen have advanced responses to the objection: Yates’s response proposes...     

Identification of planar defects in D019 phases using high-resolution transmission electron microscopy

An analysis based on crystal symmetry and high-resolution transmission electron microscopy (HRTEM) is presented as a general methodology to identify planar defects on the basal planes of D0₁₉ compounds. As a starting point, the possible (close-packing preserving) planar defects are classified in accordance with their visibility, and the magnitude of the displacement vector on prismatic projections. Analysis of experimental HRTEM images, obtained under two different viewing conditions, followed by matching with simulated images, enables unambiguous identification to be made. The methodology is applied to planar defects observed in D0₁₉ Co₃     

A comparison of the correlational structures and elevation patterns of the MMPI-2 restructured clinical (RC) and clinical scales

The relationship between the MMPI-2 restructured clinical scales and the original clinical scales was evaluated using an outpatient clinical sample (N = 150). Similar patterns of correlations to those reported by Tellegen et al. in 2003, such as high correlations between the restructured scales and their original scale counterparts and lower intercorrelations among the restructured scales than among the original scales, were found in the outpatient sample. The former provided evidence of convergence between the two sets of scales, whereas the latter increases the potential for discriminant validity in the restructured scale profiles. Mean T-scores of the restructured scales were significantly lower than their original scale counterparts for every clinical scale except Scale 1 (hypochondriasis). Individual profiles exhibited fewer scale elevations using the restructured clinical scales (M = 2.15, Mdn = 2.0) than the original clinical scales (M = 3.29, Mdn = 3.0). The majority of client profiles (56%) had fewer scale elevations when plotted using the restructured scales versus the original clinical scales.     

Comparison of scotopic sensitivity in diurnal (Anas platyrhynchos) and crepuscular (Dendrocygna autumnalis) ducks.

Scotopic visual adaptation curves were obtained from 4 mallard ducks. A curve of best fit was used to compare the mallards' mean adaptation curve to the curve previously reported for the black-bellied tree duck, a crepuscular species. The curves did not differ significantly in either their slopes or base levels (thresholds). The mallards curve had a rod-cone "break" at approximately 25 min. This break is evident in the scotopic curve for pigeons, but is absent from the black-bellied tree ducks' curve. Examination of retinal tissues indicated that the black-bellied tree ducks had significantly more rods and cones, and a larger rod:cone ratio than the mallards. The mallards' scotopic visual threshold is exceeded by the natural illumination present under several nocturnal conditions.     

Comparison of dynamic (effortful) touch by hand and foot

Spatial perception by dynamic touch is a well-documented capability of the hand and arm. Morphological and physiological characteristics of the foot and leg suggest that such a capability may not generalize to that putatively less dexterous limb. The authors examined length perception by dynamic touch in a task in which weighted aluminum rods were grasped by the hand and wielded about the wrist or secured to the foot and wielded about the ankle. Participants' (N = 10) upper and lower extremities were comparable in terms of (a) the accuracy and consistency of length perception and (b) their sensitivity to manipulations of the moments of the mass distribution of the rods. The authors discuss those results in terms of the field-like structure of the haptic perceptual system, an organization that may underlie what appears to be functional, rather than anatomical, specificity.     

Comparison of grouping abilities in humans (Homo sapiens) and baboons (Papio papio) with the Ebbinghaus illusion

This research comparatively assessed grouping mechanisms of humans (n = 8) and baboons (n = 8) in an illusory task that employs configurations of target and surrounding circles arranged to induce the Ebbinghaus (Titchener) illusion. Analyses of response behaviors and points of subjective equality demonstrated that only humans misjudged the central target size under the influence of the Ebbinghaus illusion, whereas baboons expressed a more veridical perception of target sizes. It is argued that humans adopted a global mode of stimulus processing of the illusory figure in our task that has favored the illusion. By contrast, a strong local mode of stimulus processing with attention restricted to the target must have prevented illusory effects in baboons. These findings suggest that monkeys and humans have evolved modes of object recognition that do not similarly rely on the same gestalt principles.     

The biological week and broader time structures (chronomes): in memory of Gunther Hildebrandt

Data illustrating the biological week and chronomes are presented in recognition of extensive work of G. Hildebrandt.