Search results for "twinning"
showing 10 items of 33 documents
eTwinning Collaborative Learning Environment in Initial Teacher Education
2018
This paper aims to describe the eTwinning Teacher Training Institutes Pilot (TTI)1experiment during academic year 2014/15 with 550 undergraduate students from first and second year of Educational Technologies degree courses. The research was given start with the purpose of preparing tomorrow's teachers for a future where the use of ICT and is in everyday teaching, to promote their digital skills and communication skills, and their use of English as a foreign language within a cross-cultural context. The teaching presence was proved through proper supervision and the emergence of mutual support from 36 tutors and 550 students. The results of the research contributed to our understanding of h…
Influence of twinned structure on the morphology of CdTe(111) layers grown by MOCVD on GaAs(100) substrates
2003
Abstract The morphology and structure of CdTe(1 1 1) layers grown on GaAs(1 0 0) by MOCVD have been studied by atomic force microscopy (AFM) and X-ray texture analysis. Growth conditions have been chosen so that mirror-like CdTe layers are obtained. Layers whose growth times vary between 10 s and 2 h have been investigated. The X-ray texture analysis shows that the CdTe layers grown on GaAs substrates that were thermally treated at 580°C for 30 min in a H 2 atmosphere exhibit a (1 1 1) preferential orientation and are twinned. This twinned structure of the (1 1 1)CdTe layer which is observed as 60° rotated triangular crystallites in the AFM images strongly influences the surface morphology.…
Structural characterization of CdTe layers grown on (0001) sapphire by MOCVD
2004
Abstract We report on the growth of CdTe layers directly onto (0 0 0 1) sapphire substrates by MOCVD. The structure and morphology of the layers have been investigated as a function of growth temperature and II/VI precursor molar ratio by X-ray diffraction and scanning electron microscopy. The texture of the samples has revealed the existence of a temperature threshold, with higher growth temperatures resulting on completely (1 1 1) oriented layers. Some of these layers contained microtwins, as indicated by the extra peaks in the {4 2 2} Φ scans, leading to the existence of two different domains. The structural quality of each domain, as well as of the sample as a whole, has been determined…
Protein-induced, previously unidentified twin form of calcite.
2007
Using single-crystal x-ray diffraction, we found a formerly unknown twin form in calcite crystals grown from solution to which a mollusc shell-derived 17-kDa protein, Caspartin, was added. This intracrystalline protein was extracted from the calcitic prisms of the Pinna nobilis shells. The observed twin form is characterized by the twinning plane of the (108)-type, which is in addition to the known four twin laws of calcite identified during 150 years of investigations. The established twin forms in calcite have twinning planes of the (001)-, (012)-, (104)-, and (018)-types. Our discovery provides additional evidence on the crucial role of biological macromolecules in biomineralization.
Crystal Inclusions in Diamonds and Other Crystals
2013
Single crystal inclusions in natural single crystals bear a lot of information on the genesis and phase stabilities between host and guest crystals. Not only parameters of the natural environment of crystallization may be elucidated, also the history of up-rise within the earth to the surface and the development during procedures, eventually applied by mankind to enhance the physical properties of crystals, may be detectable. Structural reactions resulting in phase separation due to chemical stress during change of physical parameters shed light on the borders of solid solution and exsolution domains. Natural crystals of proper quality allow us to evaluate a time factor in phase stabilities…
Micro-structure evolution of wall based crystals after casting of model suspensions as obtained from Bragg microscopy.
2012
Growth of heterogeneously nucleated, wall based crystals plays a major role in determining the micro-structure during melt casting. This issue is here addressed using a model system of charged colloidal spheres in deionized aqueous suspension observed by Bragg microscopy which is a combination of light scattering and microscopy. We examine the evolution of the three-dimensional size, shape, and orientation of twin domains in monolithic crystals growing from two opposing planar walls into a meta-stable (shear-) melt. At each wall crystal orientation and twinning emerges during nucleation with small domains. During growth these widen and merge. From image analysis we observe the lateral coars…
Structural factor in bending testing of fivefold twinned nanowires revealed by finite element analysis
2016
In this study, we performed finite element method simulations to investigate the effect of the structure on the elastic response of Ag and Au nanowires (NWs) with a fivefold twinned crystal structure in bending tests. Two different models of a pentagonal NW were created: a 'uniform model' having an isotropic continuous structure and a 'segmented model' consisting of five anisotropic domains. Two asymmetrical mechanical test configurations were simulated: cantilevered beam bending and 3-point bending. The dimensions of the NW, the test configurations, as well as the force and the displacement ranges were based on the previously obtained experimental data. The results of the simulations demon…
Twin coarsening in CdTe(111) films grown on GaAs(100)
2006
Abstract We present a scanning force microscopy study of twin coarsening in CdTe(1 1 1) films grown on GaAs(1 0 0). Two types of CdTe(1 1 1) twins grow epitaxially and with equal probability on the long-range wavy surface structure developed by previous in situ annealing of the GaAs(1 0 0) substrate. Due to this initial substrate wavy structure, the grain coarsening during film growth leads to a quasi-one-dimensional rippled pattern. We propose a coarsening mechanism between twins driven by the formation of stacking faults.
Experimentally Induced Twinning in Plants
1955
IT is well known that characteristic changes in leaf-form and growth habit can be induced by treating shoot apices with synthetic growth substances. The question arises as to whether entire plant embryos also can be induced to develop abnormally by the action of growth regulators. For this purpose the solutions must be applied in a suitable manner to the earliest embryo stages through the growing carpel walls, or it would be necessary to remove the still quite small embryos and to expose them in vitro to the proper influences. Both methods are difficult to apply and have as yet proved unsatisfactory.
Prematurity and twinning
2012
Aim of the study: Newborns from multiple pregnancies are increasing in number and demonstrate a higher perinatal morbidity and mortality compared to singletons. Prematurity is the main reason for most neonatal diseases in twins, but other variables may play a role and their prenatal evaluation may improve the overall outcome. Main findings: Prematurity is six times more frequent in twins and therefore birth weight is significantly lower compared to singletons. Thus, twins are more exposed to prematurity related diseases (respiratory, cardiovas- cular, infectious, etc.) and to long-term complications (especially neurological disabilities). Results: It is very difficult to estimate the increa…