497 research outputs found
Structure factors of harmonic and anharmonic Fibonacci chains by molecular dynamics simulations
The dynamics of quasicrystals is characterized by the existence of phason
excitations in addition to the usual phonon modes. In order to investigate
their interplay on an elementary level we resort to various one-dimensional
model systems. The main observables are the static, the incoherent, and the
coherent structure factor, which are extracted from molecular dynamics
simulations. For the validation of the algorithms, results for the harmonic
periodic chain are presented. We then study the Fibonacci chain with harmonic
and anharmonic interaction potentials. In the dynamic Fibonacci chain
neighboring atoms interact by double-well potentials allowing for phason flips.
The difference between the structure factors of the dynamic and the harmonic
Fibonacci chain lies in the temperature dependence of the phonon line width. If
a bias is introduced in the well depth, dispersionless optic phonon bands split
off.Comment: 12 pages, 15 figure
The local atomic quasicrystal structure of the icosahedral Mg25Y11Zn64 alloy
A local and medium range atomic structure model for the face centred
icosahedral (fci) Mg25Y11Zn64 alloy has been established in a sphere of r = 27
A. The model was refined by least squares techniques using the atomic pair
distribution (PDF) function obtained from synchrotron powder diffraction. Three
hierarchies of the atomic arrangement can be found: (i) five types of local
coordination polyhedra for the single atoms, four of which are of Frank-Kasper
type. In turn, they (ii) form a three-shell (Bergman) cluster containing 104
atoms, which is condensed sharing its outer shell with its neighbouring
clusters and (iii) a cluster connecting scheme corresponding to a
three-dimensional tiling leaving space for few glue atoms. Inside adjacent
clusters, Y8-cubes are tilted with respect to each other and thus allow for
overall icosahedral symmetry. It is shown that the title compound is
essentially isomorphic to its holmium analogue. Therefore fci-Mg-Y-Zn can be
seen as the representative structure type for the other rare earth analogues
fci-Mg-Zn-RE (RE = Dy, Er, Ho, Tb) reported in the literature.Comment: 12 pages, 8 figures, 2 table
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Socioeconomic Mediators of Racial and Ethnic Disparities in Congenital Heart Disease Outcomes: A Population-Based Study in California.
Background Racial/ethnic and socioeconomic disparities exist in outcomes for children with congenital heart disease. We sought to determine the influence of race/ethnicity and mediating socioeconomic factors on 1-year outcomes for live-born infants with hypoplastic left heart syndrome and dextro-Transposition of the great arteries. Methods and Results The authors performed a population-based cohort study using the California Office of Statewide Health Planning and Development database. Live-born infants without chromosomal anomalies were included. The outcome was a composite measure of mortality or unexpected hospital readmissions within the first year of life defined as >3 (hypoplastic left heart syndrome) or >1 readmissions (dextro-Transposition of the great arteries). Hispanic ethnicity was compared with non-Hispanic white ethnicity. Mediation analyses determined the percent contribution to outcome for each mediator on the pathway between race/ethnicity and outcome. A total of 1796 patients comprised the cohort (n=964 [hypoplastic left heart syndrome], n=832 [dextro-Transposition of the great arteries]) and 1315 were included in the analysis (n=477 non-Hispanic white, n=838 Hispanic). Hispanic ethnicity was associated with a poor outcome (crude odds ratio, 1.72; 95% confidence interval [CI], 1.37-2.17). Higher maternal education (crude odds ratio 0.5; 95% CI , 0.38-0.65) and private insurance (crude odds ratio, 0.65; 95% CI , 0.45-0.71) were protective. In the mediation analysis, maternal education and insurance status explained 33.2% (95% CI , 7-66.4) and 27.6% (95% CI , 6.5-63.1) of the relationship between race/ethnicity and poor outcome, while infant characteristics played a minimal role. Conclusions Socioeconomic factors explain a significant portion of the association between Hispanic ethnicity and poor outcome in neonates with critical congenital heart disease. These findings identify vulnerable populations that would benefit from resources to lessen health disparities
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Initial Metabolic Profiles Are Associated with 7-Day Survival among Infants Born at 22-25 Weeks of Gestation.
OBJECTIVE:To evaluate the association between early metabolic profiles combined with infant characteristics and survival past 7 days of age in infants born at 22-25 weeks of gestation. STUDY DESIGN:This nested case-control consisted of 465 singleton live births in California from 2005 to 2011 at 22-25 weeks of gestation. All infants had newborn metabolic screening data available. Data included linked birth certificate and mother and infant hospital discharge records. Mortality was derived from linked death certificates and death discharge information. Each death within 7 days was matched to 4 surviving controls by gestational age and birth weight z score category, leaving 93 cases and 372 controls. The association between explanatory variables and 7-day survival was modeled via stepwise logistic regression. Infant characteristics, 42 metabolites, and 12 metabolite ratios were considered for model inclusion. Model performance was assessed via area under the curve. RESULTS:The final model included 1 characteristic and 11 metabolites. The model demonstrated a strong association between metabolic patterns and infant survival (area under the curve [AUC] 0.885, 95% CI 0.851-0.920). Furthermore, a model with just the selected metabolites performed better (AUC 0.879, 95% CI 0.841-0.916) than a model with multiple clinical characteristics (AUC 0.685, 95% CI 0.627-0.742). CONCLUSIONS:Use of metabolomics significantly strengthens the association with 7-day survival in infants born extremely premature. Physicians may be able to use metabolic profiles at birth to refine mortality risks and inform postnatal counseling for infants born at <26 weeks of gestation
Second harmonic generation on incommensurate structures: The case of multiferroic MnWO4
A comprehensive analysis of optical second harmonic generation (SHG) on an
incommensurate (IC) magnetically ordered state is presented using multiferroic
MnWO4 as model compound. Two fundamentally different SHG contributions coupling
to the primary IC magnetic order or to secondary commensurate projections of
the IC state, respectively, are distinguished. Whereas the latter can be
described within the formalism of the 122 commensurate magnetic point groups
the former involves a breakdown of the conventional macroscopic symmetry
analysis because of its sensitivity to the lower symmetry of the local
environment in a crystal lattice. Our analysis thus foreshadows the fusion of
the hitherto disjunct fields of nonlinear optics and IC order in
condensed-matter systems
Nationwide implementation of the self-management program "Living well with COPD": Process and effectiveness evaluation using a mixed-methods approach.
To evaluate the nationwide implementation of the "Living well with COPD" program by the Swiss Lung Association in various cantons in Switzerland.
For the process evaluation, we used qualitative (interview, focus group) and quantitative (questionnaires, documentation analysis) methods to assess the implementation outcomes reach, dose, fidelity and acceptability. For the effectiveness, we performed a pre-post analysis of patient data collected at baseline and program end (after 14 months).
Seven Cantonal Lung Associations implemented the program into their services according to plan, conducted it 13 times and included 122 COPD patients. Patients' attendance rate was 81% and coaches' fidelity to protocol 94%. Acceptance and satisfaction of all involved persons was high. Integration of the coaches' additional workload, uncertainties regarding roles and responsibilities and sustainable reimbursement were major challenges. Patients significantly improved in COPD specific quality of life and increased exercise capacity with on average 3.2 more repetitions in the 1-minute sit-to-stand test.
The program was successfully implemented throughout Switzerland with high acceptability and positive association with patients' quality of life.
Our findings support the broader multiplication throughout Switzerland and serves the international community since it is one of the first nationwide implementations beyond study settings
Overlapping Unit Cells in 3d Quasicrystal Structure
A 3-dimensional quasiperiodic lattice, with overlapping unit cells and
periodic in one direction, is constructed using grid and projection methods
pioneered by de Bruijn. Each unit cell consists of 26 points, of which 22 are
the vertices of a convex polytope P, and 4 are interior points also shared with
other neighboring unit cells. Using Kronecker's theorem the frequencies of all
possible types of overlapping are found.Comment: LaTeX2e, 11 pages, 5 figures (8 eps files), uses iopart.class. Final
versio
A quasi-unit cell model for Al-Ni-Co Ideal Quasicrystal based on clusters with broken 10-fold symmetry
We present new evidence supporting the quasi-unit cell description of the
decagonal quasicrystal which shows that the solid is
composed of repeating, overlapping decagonal cluster columns with broken
10-fold symmetry. We propose an atomic model which gives a significantly
improved fit to electron microscopy experiments compared to a previous proposal
by us and to alternative proposals with 10-fold symmetric clusters.Comment: 4 pages, 4 eps figures, use epsfig.sty and revtex revised text and
figure
Digital Strategies in Action – a Comparative Analysis of National Data Infrastructure Development
In recent years, many countries have started to draft strategies and policies related to the data economy. To support new data-driven activities and innovations, the development of a national data infrastructure (NDI) is seen as key. The concept of NDI has entered governmental strategic discussions on data as an asset, the role of data infrastructures in innovation and economic activity, and the role of government therein. However, there is a gap between the ambitions as laid out in the strategies and the actual actions taken towards realizing them. To understand this gap and support NDI development, insight is needed in the components and processes of realizing NDI strategies. In this paper, we study NDI strategies 'in action' in the Netherlands and Switzerland using an analytical framework comprising strategies, stakeholders, design, components and governance. Special emphasis is put on the role of government in formulating and implementing strategies. Our cross-case analysis uncovers lessons that seem relevant for NDI development elsewhere, as well as challenges that need to be resolved before NDIs can hope actually make the impact associated with them
Bistability, multistability and nonreciprocal light propagation in Thue-Morse multilayered structures
The nonlinear properties of quasiperiodic photonic crystals based on the
Thue-Morse sequence are investigated. The intrinsic spatial asymmetry of these
one-dimensional structures for odd generation numbers results in bistability
thresholds which are sensitive to the propagation direction. Along with
resonances of perfect transmission, this feature allows to achieve strongly
non-reciprocal propagation and to create an all-optical diode. The salient
qualitative features of such optical diode action is readily explained through
a simple coupled resonator model. The efficiency of a passive scheme, which
does not necessitate of an additional short pump signal, is compared to an
active scheme, where such a signal is required.Comment: 18 pages, 8 figure
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