1,468 research outputs found
Formation of a Metallic Contact: Jump to Contact Revisited
The transition from tunneling to metallic contact between two surfaces does
not always involve a jump, but can be smooth. We have observed that the
configuration and material composition of the electrodes before contact largely
determines the presence or absence of a jump. Moreover, when jumps are found
preferential values of conductance have been identified. Through combination of
experiments, molecular dynamics, and first-principles transport calculations
these conductance values are identified with atomic contacts of either
monomers, dimers or double-bond contacts.Comment: 4 pages, 5 figure
Observation of a parity oscillation in the conductance of atomic wires
Using a scanning tunnel microscope or mechanically controlled break
junctions, atomic contacts of Au, Pt and Ir are pulled to form chains of atoms.
We have recorded traces of conductance during the pulling process and averaged
these for a large amount of contacts. An oscillatory evolution of conductance
is observed during the formation of the monoatomic chain suggesting a
dependence on even or odd numbers of atoms forming the chain. This behaviour is
not only present in the monovalent metal Au, as it has been previously
predicted, but is also found in the other metals which form chains suggesting
it to be a universal feature of atomic wires
Patient-specific CFD simulation of intraventricular haemodynamics based on 3D ultrasound imaging
Background: The goal of this paper is to present a computational fluid dynamic (CFD) model with moving boundaries to study the intraventricular flows in a patient-specific framework. Starting from the segmentation of real-time transesophageal echocardiographic images, a CFD model including the complete left ventricle and the moving 3D mitral valve was realized. Their motion, known as a function of time from the segmented ultrasound images, was imposed as a boundary condition in an Arbitrary Lagrangian-Eulerian framework.
Results: The model allowed for a realistic description of the displacement of the structures of interest and for an effective analysis of the intraventricular flows throughout the cardiac cycle. The model provides detailed intraventricular flow features, and highlights the importance of the 3D valve apparatus for the vortex dynamics and apical flow.
Conclusions: The proposed method could describe the haemodynamics of the left ventricle during the cardiac cycle. The methodology might therefore be of particular importance in patient treatment planning to assess the impact of mitral valve treatment on intraventricular flow dynamics
Developing reference material for validation of hair spectral analysis reliability
Mineral analysis of human hair is increasingly proposed as a estimation method for the human contamination with environmental mineral pollutants and even as a diagnostic tool for related health problems. It offers a good way of investigating long-term variation in trace element concentration. Many minor and trace elements can be determined in hair samples with good precision and sensitivity by a variety of analytical techniques. An important requirement in such work is the application of suitable analytical quality control, for which the availability of a hair reference material is important. In paper the preparation of the human hair reference material and the initial stages which were taken to confirm its certification are described
Transfer from implicit to explicit phonological abilities in first and second language learners
Children's abilities to process the phonological structure of words are important predictors of their literacy development. In the current study, we examined the interrelatedness between implicit (i.e., speech decoding) and explicit (i.e., phonological awareness) phonological abilities, and especially the role therein of lexical specificity (i.e., the ability to learn to recognize spoken words based on only minimal acoustic-phonetic differences). We tested 75 Dutch monolingual and 64 Turkish–Dutch bilingual kindergartners. SEM analyses showed that speech decoding predicted lexical specificity, which in turn predicted rhyme awareness in the first language learners but phoneme awareness in the second language learners. Moreover, in the latter group there was an impact of the second language: Dutch speech decoding and lexical specificity predicted Turkish phonological awareness, which in turn predicted Dutch phonological awareness. We conclude that language-specific phonological characteristics underlie different patterns of transfer from implicit to explicit phonological abilities in first and second language learners
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