1,454 research outputs found
A random matrix approach to decoherence
In order to analyze the effect of chaos or order on the rate of decoherence
in a subsystem, we aim to distinguish effects of the two types of dynamics by
choosing initial states as random product states from two factor spaces
representing two subsystems. We introduce a random matrix model that permits to
vary the coupling strength between the subsystems. The case of strong coupling
is analyzed in detail, and we find no significant differences except for very
low-dimensional spaces.Comment: 11 pages, 5 eps-figure
De Novo Occurrence of a Variant in ARL3 and Apparent Autosomal Dominant Transmission of Retinitis Pigmentosa.
BackgroundRetinitis pigmentosa is a phenotype with diverse genetic causes. Due to this genetic heterogeneity, genome-wide identification and analysis of protein-altering DNA variants by exome sequencing is a powerful tool for novel variant and disease gene discovery. In this study, exome sequencing analysis was used to search for potentially causal DNA variants in a two-generation pedigree with apparent dominant retinitis pigmentosa.MethodsVariant identification and analysis of three affected members (mother and two affected offspring) was performed via exome sequencing. Parental samples of the index case were used to establish inheritance. Follow-up testing of 94 additional retinitis pigmentosa pedigrees was performed via retrospective analysis or Sanger sequencing.Results and conclusionsA total of 136 high quality coding variants in 123 genes were identified which are consistent with autosomal dominant disease. Of these, one of the strongest genetic and functional candidates is a c.269A>G (p.Tyr90Cys) variant in ARL3. Follow-up testing established that this variant occurred de novo in the index case. No additional putative causal variants in ARL3 were identified in the follow-up cohort, suggesting that if ARL3 variants can cause adRP it is an extremely rare phenomenon
Signatures of the correlation hole in total and partial cross sections
In a complex scattering system with few open channels, say a quantum dot with
leads, the correlation properties of the poles of the scattering matrix are
most directly related to the internal dynamics of the system. We may ask how to
extract these properties from an analysis of cross sections. In general this is
very difficult, if we leave the domain of isolated resonances. We propose to
consider the cross correlation function of two different elastic or total cross
sections. For these we can show numerically and to some extent also
analytically a significant dependence on the correlations between the
scattering poles. The difference between uncorrelated and strongly correlated
poles is clearly visible, even for strongly overlapping resonances.Comment: 25 pages, 13 Postscript figures, typos corrected and references adde
Fidelity and Purity Decay in Weakly Coupled Composite Systems
We study the stability of unitary quantum dynamics of composite systems (for
example: central system + environment) with respect to weak interaction between
the two parts. Unified theoretical formalism is applied to study different
physical situations: (i) coherence of a forward evolution as measured by purity
of the reduced density matrix, (ii) stability of time evolution with respect to
small coupling between subsystems, and (iii) Loschmidt echo measuring dynamical
irreversibility. Stability has been measured either by fidelity of pure states
of a composite system, or by the so-called reduced fidelity of reduced density
matrices within a subsystem. Rigorous inequality among fidelity,
reduced-fidelity and purity is proved and a linear response theory is developed
expressing these three quantities in terms of time correlation functions of the
generator of interaction. The qualitatively different cases of regular
(integrable) or mixing (chaotic in the classical limit) dynamics in each of the
subsystems are discussed in detail. Theoretical results are demonstrated and
confirmed in a numerical example of two coupled kicked tops.Comment: 21 pages, 12 eps figure
Homogeneous Gold Catalysis through Relativistic Effects: Addition of Water to Propyne
In the catalytic addition of water to propyne the Au(III) catalyst is not
stable under non-relativistic conditions and dissociates into a Au(I) compound
and Cl2. This implies that one link in the chain of events in the catalytic
cycle is broken and relativity may well be seen as the reason why Au(III)
compounds are effective catalysts.Comment: 12 pages, 3 figures, 1 tabl
Sturmian morphisms, the braid group B_4, Christoffel words and bases of F_2
We give a presentation by generators and relations of a certain monoid
generating a subgroup of index two in the group Aut(F_2) of automorphisms of
the rank two free group F_2 and show that it can be realized as a monoid in the
group B_4 of braids on four strings. In the second part we use Christoffel
words to construct an explicit basis of F_2 lifting any given basis of the free
abelian group Z^2. We further give an algorithm allowing to decide whether two
elements of F_2 form a basis or not. We also show that, under suitable
conditions, a basis has a unique conjugate consisting of two palindromes.Comment: 25 pages, 4 figure
Enabling magnetic resonance imaging of hollow-core microstructured optical fibers via nanocomposite coating
Optical fibers are widely used in bioimaging systems as flexible endoscopes
capable of low-invasive penetration inside hollow tissue cavities. Here, we
report on the technique which allows magnetic resonance imaging (MRI) of
hollow-core microstructured fibers (HC-MFs), paving the way for combing MRI and
optical bioimaging. Our approach is based on Layer-by-Layer assembly of
oppositely charged polyelectrolytes and magnetite nanoparticles on the inner
core surface of HC-MFs. Incorporation of magnetite nanoparticles into
polyelectrolyte layers renders HC-MFs visible for MRI and induces the red-shift
in their transmission spectra. Specifically, the transmission shifts up to 60
nm have been revealed for the several-layers composite coating along with the
high-quality contrast of HC-MFs in MRI scans. Our results shed light on
marrying fiber-based endoscopy with MRI that opens novel possibilities for
minimally invasive clinical diagnostics and surgical procedures in vivo.Comment: 11 pages, 6 figure
Correlation functions of scattering matrix elements in microwave cavities with strong absorption
The scattering matrix was measured for microwave cavities with two antennas.
It was analyzed in the regime of overlapping resonances. The theoretical
description in terms of a statistical scattering matrix and the rescaled
Breit-Wigner approximation has been applied to this regime. The experimental
results for the auto-correlation function show that the absorption in the
cavity walls yields an exponential decay. This behavior can only be modeled
using a large number of weakly coupled channels. In comparison to the
auto-correlation functions, the cross-correlation functions of the diagonal
S-matrix elements display a more pronounced difference between regular and
chaotic systems
Structural changes in FeOx/γ-Al2O3 catalysts during ethylbenzene dehydrogenation
The structural changes that occur in a FeOx/γ-Al2O3 catalyst during the dehydrogenation of ethylbenzene in a fluidized CREC Riser Simulator have been investigated. Chemical and morphological changes are observed to take place as a result of reaction. Electron microscopy reveals the formation of needle-like alumina structures apparently enclosing iron oxide particles. The formation of such structures at relatively low temperatures is unexpected and has not previously been reported. Additionally, X-ray diffraction and Mössbauer spectroscopy confirmed the reduction of the oxidation state of iron, from Fe2O3 (haematite) to Fe3O4 (magnetite). Iron carbides, Fe3C and ɛ-Fe2C, were detected by electron microscopy through electron diffraction and lattice fringes analysis. Carbon deposition (coking) on the catalyst surface also occurs. The observed structural changes are likely to be closely correlated with the catalytic properties of the materials, in particular with catalyst deactivation, and thereby provide important avenues for future study of this industrially important reaction. Fe2O3/Al2O3 catalyst undergoes chemical and morphological changes during ethylbenzene dehydrogenation forming Al2O3 needles which appear to contain reduced Fe3O4 particles. Fe3C also forms during reaction
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