Search results for "defect"
showing 10 items of 879 documents
FMEA - BASIC CONCEPT IN PRODUCT QUALITY
2018
Failure modes and effects analysis (FMEA) is a systematic procedure for analyzing a system (the entire system or just an assembly, subassembly or component) to identify potential failure modes, causes and effects of each failure on system operation. A somewhat different definition was formulated by Goddard Space Flight Center (USA) : FMEA is a procedure whereby every credible way of defeating each item from the lower decomposition level to the highest level is analyzed to determine effects on the system and classify each potential way of failure according to the severity of its effect.
Defects in yttrium aluminium perovskite and garnet crystals: atomistic study
2000
Native and impurity point defects in both yttrium aluminium perovskite (YAP) and garnet (YAG) crystals are studied in the framework of the pair-potential approximation coupled with the shell model description of the lattice ions. The calculated formation energies for native defects suggest that the antisite disorder is preferred over the Frenkel and Schottky-like disorder in both YAP and YAG. The calculated values of the distortion caused by the antisite YAl x in the lattice turn out to be in an excellent agreement with the EXAFS measurements. In non-stoichiometric compounds, the calculated reaction energies indicate that excess Y2 O3 or Al2 O3 is most likely to be accommodated by the forma…
Phenotypic analysis of individuals with Costello syndrome due to HRAS p.G13C.
2011
Costello syndrome is characterized by severe failure-to-thrive, short stature, cardiac abnormalities (heart defects, tachyarrhythmia, and hypertrophic cardiomyopathy (HCM)), distinctive facial features, a predisposition to papillomata and malignant tumors, postnatal cerebellar overgrowth resulting in Chiari 1 malformation, and cognitive disabilities. De novo germline mutations in the proto-oncogene HRAS cause Costello syndrome. Most mutations affect the glycine residues in position 12 or 13, and more than 80% of patients share p.G12S. To test the hypothesis that subtle genotype-phenotype differences exist, we report the first cohort comparison between 12 Costello syndrome individuals with p…
Dynamic tuning of the director field in liquid crystal shells using block copolymers
2020
When an orientationally ordered system, like a nematic liquid crystal (LC), is confined on a self-closing spherical shell, topological constraints arise with intriguing consequences that depend critically on how the LC is aligned in the shell. We demonstrate reversible dynamic tuning of the alignment, and thereby the topology, of nematic LC shells stabilized by the nonionic amphiphilic block copolymer Pluronic F127. Deep in the nematic phase, the director (the average molecule orientation) is tangential to the interface, but upon approaching the temperature TNI of the nematic– isotropic transition, the director realigns to normal. We link this to a delicate interplay between an interfacial …
UV-Photoinduced Defects In Ge-Doped Optical Fibers
2005
We investigated the effect of continuous-wave (cw) UV laser radiation on single-mode Ge-doped H2- loaded optical fibers. An innovative technique was developed to measure the optical absorption (OA) induced in the samples by irradiation, and to study its dependence from laser fluence. The combined use of the electron spin resonance (ESR) technique allowed the structural identification of several radiation-induced point defects, among which the Ge(1) (GeO4 -) is found to be responsible of induced OA in the investigated spectral region.
Structure, nanohardness and photoluminescence of ZnO ceramics based on nanopowders
2015
ZnO ceramics obtained from grained powders with different grain size by hot pressing and ceramics from tetrapods nanopowders obtained by press-less sintering have been investigated under identical conditions. Ceramics obtained by hot pressing were optically transparent but were composed of large inhomogeneous grains (d = 8–35 μm) exhibiting a substructure. Decreased values of elastic modulus within a grain and a wide defect-associated ('green') photoluminescence (PL) band at 2.2–2.8 eV in conjunction with a weak excitonic band indicate a high concentration of residual point defects in hot pressed ZnO ceramics. Utilization of more small-grained powders contributes to the formation of more un…
Effect of aneurysm on the mechanical dissection properties of the human ascending thoracic aorta
2012
Objectives: The acute dissection of an ascending thoracic aortic aneurysm (ATAA) represents a devastating separation of elastic layers occurring when the hemodynamic loads on the diseased wall exceed the adhesive strength between layers. At present, the mechanics underlying aortic dissection are largely unclear, and the biomechanical delamination properties of the aneurysmal aorta are not defined. Individuals with bicuspid aortic valve (BAV) are particularly predisposed to ascending aortic aneurysm formation, with a marked risk of aortic dissection. The purpose of this study was to evaluate and compare the dissection properties of nonaneurysmal and aneurysmal human ascending thoracic aorta …
The aristaless (Arx) gene: one gene for many "interneuronopathies".
2009
The ARX (Aristaless-related (X-linked) homeobox) gene is not only present in arthropods and their ancestors, but also in vertebrates including humans (ARX orthologs). The gene is composed of 5 coding exons and it is expressed predominantly in foetal and adult brain and skeletal muscle. In this review we report on our experience and review the existing literature on the genotype and phenotype heterogeneity associated with ARX abnormalities in humans ranging from severe neuronal migration defects (e.g., lissencephaly), to mild forms of X-linked mental retardation without apparent brain abnormalities. The ARX-related disorders are reviewed focusing on their clinical features and on the role of…
VATER/VACTERL association: clinical variability and expanding phenotype including laryngeal stenosis.
1992
Vertebral abnormalities and anorectal and tracheoesophageal defects are the main manifestations in the VATER/VACTERL association. Radial defects vary from radial aplasia to thumb duplication. Heart and renal defects are reported with lower frequency. Additional malformations, such as the laryngeal stenosis described in the present patient, may expand the phenotype of the association. The wide spectrum of congenital abnormalities confirms the high clinical variability of VATER/VACTERL association which seems to be due to a disruption of blastogenesis. © 1992 Wiley-Liss, Inc.
Isoelectronic series of oxygen deficient centers in silica: experimental estimation of homogeneous and inhomogeneous spectral widths
2008
We report nanosecond time-resolved photoluminescence measurements on the isoelectronic series of oxygen deficient centers in amorphous silica related to silicon, germanium and tin atoms, which are responsible of fluorescence activities at approximately 4 eV under excitation at approximately 5 eV. The dependence of the first moment of their emission band on time and that of the radiative decay lifetime on emission energy are analyzed within a theoretical model able to describe the effects introduced by disorder on the optical properties of the defects. We obtain separate estimates of the homogeneous and inhomogeneous contributions to the measured emission line width, and we derive homogeneou…