3,041 research outputs found
Intermittent/transient faults in digital systems
Containment set techniques are applied to 8085 microprocessor controllers so as to transform a typical control system into a slightly modified version, shown to be crashproof: after the departure of the intermittent/transient fault, return to one proper control algorithm is assured, assuming no permanent faults occur
A statistical model approximation for perovskite solid-solutions: a Raman study of lead-zirconate-titanate single crystal
Lead titanate (PbTiO3) is a classical example of a ferroelectric perovskite
oxide illustrating a displacive phase transition accompanied by a softening of
a symmetry-breaking mode. The underlying assumption justifying the soft-mode
theory is that the crystal is macroscopically sufficiently uniform so that a
meaningful free energy function can be formed. In contrast to PbTiO3,
experimental studies show that the phase transition behaviour of
lead-zirconate-titanate solid solution (PZT) is far more subtle. Most of the
studies on the PZT system have been dedicated to ceramic or powder samples, in
which case an unambiguous soft-mode study is not possible, as modes with
different symmetries appear together. Our Raman scattering study on
titanium-rich PZT single crystal shows that the phase transitions in PZT cannot
be described by a simple soft-mode theory. In strong contrast to PbTiO3,
splitting of transverse E-symmetry modes reveals that there are different
locally-ordered regions. The role of crystal defects, random distribution of Ti
and Zr at the B-cation site and Pb ions shifted away from their ideal
positions, dictates the phase transition mechanism. A statistical model
explaining the observed peak splitting and phase transformation to a complex
state with spatially varying local order in the vicinity of the morphotropic
phase boundary is given.Comment: Article contains four black-and-white figures, one colour figure and
one Table. Symmetry analysis and details of the model are given in Appendices
I and II, respectivel
Low temperature superlattice in monoclinic PZT
TEM has shown that the strongly piezoelectric material Pb(Zr0.52Ti0.48)O3
separates into two phases at low temperatures. The majority phase is the
monoclinic phase previously found by x-ray diffraction. The minority phase,
with a nanoscale coherence length, is a slightly distorted variant of the first
resulting from the anti-phase rotation of the oxygen octahedra about [111].
This work clears up a recent controversy about the origin of superlattice peaks
in these materials, and supports recent theoretical results predicting the
coexistence of ferroelectric and rotational instabilities.Comment: REVTeX4, 4 eps figures embedded. JPG version of figs. 2&4 is also
include
Association between CD14 gene polymorphisms and disease phenotype in sarcoidosis
SummaryAlthough the etiology of sarcoidosis is unknown, genetic susceptibility has been demonstrated. Granuloma formation is a key feature in the pathophysiology of sarcoidosis and Crohn’s Disease, raising the possibility that these diseases share common pathogenetic pathways. An association between sarcoidosis and the protein “CD14”, a molecule that is part of the lipopolysaccharide (LPS) cell surface receptor complex, has been suggested.In the current study we evaluated the CD14 gene promoter 159 C→T polymorphic site and soluble CD14 levels in a cohort of 74 sarcoidosis patients compared to 85 healthy controls. We further sought to identify correlations between clinical phenotype, specific genotypes and soluble CD14 levels.We found the TT genotype to be more prevalent in the sarcoidosis patient group than in controls (p=0.03). Serum levels of soluble CD14 were higher in the sarcoidosis patients (p=0.001). Within the patient cohort, CC homozygous patients presented at an older age with milder disease as assessed with the SAC score, longer time to diagnosis, and less impairment of pulmonary function tests.Our study suggests a role of CD14 in the pathogenesis of sarcoidosis, and a clinical phenotype-genotype association. Further mechanistic and epidemiologic studies are needed in order to establish the specific role of CD14 in the etiology, pathogenesis and clinical phenotype of sarcoidosis
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