Search results for " defect"
showing 10 items of 767 documents
Positron trapping rate into vacancy clusters
1979
The trapping rate of positrons into vacancy clusters in metals has been calculated. It increases with the trap size and binding energy and approximately scales with the number of vacancies in small clusters. The phonon-mediated contribution to the trapping rate is small. The temperature dependence of the trapping process is discussed.
Ab initio simulation of yttrium oxide nanocluster formation on fcc Fe lattice
2010
Using results of density functional theory (DFT) calculations the first attempt towards the understanding of Y2O3 particles formation in oxide dispersed strengthened (ODS) ferritic–martensitic steels was performed. The present work includes modeling of single defects (O impurity atom, Fe vacancy and Y substitute atom), interaction between substituted Y atoms, Y–Fe vacancy pairs and oxygen impurity atoms in the iron matrix. The calculations have showed the repulsive interaction between the two Y substitute atoms at any separation distances that might mean that the oxygen atoms or O atoms with vacancies are required to form binding between atoms in the yttrium oxide nanoclusters.
Textures in hexatic films of nonchiral liquid crystals: Symmetry breaking and modulated phases
1994
Novel modulated textures, such as stripes and multiarmed star defects, have been observed in freely suspended films of nonchiral liquid crystals just below the smectic-$C$ to hexatic phase transition. Detailed studies using depolarized reflection microscopy suggest that the stripes are locally chiral surface splay domains of the smectic-$L$ phase, a tilted hexatic not previously identified in thermotropic liquid crystals. Line defects which form additional domain walls in the hexatic lattice lead to characteristic modulations of the basic one-dimensional stripe pattern. Inside thick circular islands, for example, stripes form circumferentially and the lines form centered 12-armed stars, res…
ChemInform Abstract: Tuning the Defect Configurations in Nematic and Smectic Liquid Crystalline Shells
2013
Thin liquid crystalline shells surrounding and surrounded by aqueous phases can be conveniently produced using a nested capillary microfluidic system, as was first demonstrated by Fernandez-Nieves et al. in 2007. By choosing particular combinations of stabilizers in the internal and external phases, different types of alignment, uniform or hybrid, can be ensured within the shell. Here, we investigate shells in the nematic and smectic phases under varying boundary conditions, focusing in particular on textural transformations during phase transitions, on the interaction between topological defects in the director field and inclusions in the liquid crystal (LC), and on the possibility to relo…
Computer modelling of radiation damage in cation sublattice of corundum
1998
Results of quantum chemical computer simulations of close Frenkel defects in corundum crystals are presented and discussed. The conclusion is drawn that the energy barrier for a back recombination up to fourth nearest neighbours is less than 0.3 eV, i.e. such pairs should be unstable at temperatures above 40 K.
Congenital heart defects in newborns with apparently isolated single gastrointestinal malformation: A retrospective study.
2015
Abstract Background Congenital gastrointestinal system malformations/abdominal wall defects (GISM) may appear as isolated defects (single or complex), or in association with multiple malformations. The high incidence of association of GISM and congenital heart defects (CHD) in patients with syndromes and malformative sequences is known, but less expected is the association of apparently isolated single GISM and CHD. The aim of this study was to investigate the frequency of CHD in newborns with isolated GISM, and the possibility to modify the diagnostic-therapeutic approach just before the onset of cardiac symptoms or complications. Methods Anamnestic, clinical, and imaging data of newborns …
Environment assisted photoconversion of luminescent surface defects in SiO 2 nanoparticles
2017
Abstract Time-resolved photoluminescence investigation on SiO 2 nanoparticles was carried out in controlled atmosphere, with the aim to discern the effects induced on the typical blue luminescence band by high power UV Nd:YAG laser photons (4.66 eV) and by some selected molecular species of the air (O 2 , N 2 , CO 2 , H 2 O). These factors ultimately determine both the brightness and photostability of the emitting defect, so as to limit the unique and attracting potentialities offered by this system in many applicative fields. Here it is highlighted that the effects due to photons and molecules, singularly considered, are not additive, the radiation being more dramatic in reducing the emiss…
HIGH-PRECISION MONTE CARLO DETERMINATION OF α/ν IN THE 3D CLASSICAL HEISENBERG MODEL
1994
To study the role of topological defects in the three-dimensional classical Heisenberg model we have simulated this model on simple cubic lattices of size up to 803, using the single-cluster Monte Carlo update. Analysing the specific-heat data of these simulations, we obtain a very accurate estimate for the ratio of the specific-heat exponent with the correlation-length exponent, α/ν, from a usual finite-size scaling analysis at the critical coupling Kc. Moreover, by fitting the energy at Kc, we reduce the error estimates by another factor of two, and get a value of α/ν, which is comparable in accuracy to best field theoretic estimates.
Relative incidence and mortality of congenital heart defects diagnosed by angiohemodynamic methods: a 17-year study.
1992
Over a 17-year period (January 1971 to January 1988), 2322 children, aged 0-14 years, were diagnosed as having congenital heart disease (CHD) by cardiac catheterization and angiography. Excluding those with highly complex or undiagnosed defects, there were 2156 children with CHD, 72.4% of whom were treated surgically, with a total surgical mortality rate of 24.1%. After a mean follow-up of 9 years the overall mortality of the cohort was 29.9%, 29.1% occurring in the first month of life, 39.6% between 1 month and 1 year, and 31.2% between 1 and 14 years. The incidence, mortality, and age at death of each cardiac defect are presented and compared with the results of other studies. The overall…
Regular Horizontal Patterning on Colloidal Crystals Produced by Vertical Deposition
2009
Colloidal particles have proved to be a suitable precursor to the formation of nanoscaled materials. More explicitly, they are a suitable way to create photonic band gap materials in 3D. Several methods have been developed to assemble colloidal multilayer systems, and have yielded various levels of success. The vertical deposition method has shown itself to be one of the best in terms of time, control of the final product, crystal size and homogeneity. Despite this, the resulting crystals often present point defects, dislocations, cracks and polycrystallinity, as well as a horizontal modulation of film thickness. These defects compromise the possible utilities of the crystals. The study of …