76,914 research outputs found
Surface-confined 2D polymerization of a brominated copper-tetraphenylporphyrin on Au(111)
A coupling-limited approach for the Ullmann reaction-like on-surface
synthesis of a two-dimensional covalent organic network starting from a
halogenated metallo-porphyrin is demonstrated.
Copper-octabromo-tetraphenylporphyrin molecules can diffuse and self-assemble
when adsorbed on the inert Au(111) surface. Splitting-off of bromine atoms
bonded at the macrocyclic core of the porphyrin starts at room temperature
after the deposition and is monitored by X-ray photoelectron spectroscopy for
different annealing steps. Direct coupling between the reactive carbon sites of
the molecules is, however, hindered by the molecular shape. This leads
initially to an ordered non-covalently interconnected supramolecular structure.
Further heating to 300{\deg}C and an additional hydrogen dissociation step is
required to link the molecular macrocycles via a phenyl group and form large
ordered polymeric networks. This approach leads to a close-packed covalently
bonded network of overall good quality. The structures are characterized using
scanning tunneling microscopy. Different kinds of lattice defects and,
furthermore, the impact of polymerization on the HOMO-LUMO gap are discussed.
Density functional theory calculations corroborate the interpretations and give
further insight into the adsorption of the debrominated molecule on the surface
and the geometry and coupling reaction of the polymeric structure.Comment: 9 pages, 6 figure
CX3CR1 Polymorphisms are associated with atopy but not asthma in German children
Chemokines and their receptors are involved in many aspects of immunity. Chemokine CX3CL1, acting via its receptor CX3CR1, regulates monocyte migration and macrophage differentiation as well as T cell-dependent inflammation. Two common, nonsynonymous polymorphisms in CX3CR1 have previously been shown to alter the function of the CX3CL1/CX3CR1 pathway and were suggested to modify the risk for asthma. Using matrix-assisted laser desorption/ionization time-of-flight technology, we genotyped polymorphisms Val249Ile and Thr280Met in a cross-sectional population of German children from Munich (n = 1,159) and Dresden ( n = 1,940). For 249Ile an odds ratio of 0.77 (95% confidence interval 0.63-0.96; p = 0.017) and for 280Met an odds ratio of 0.71 ( 95% confidence interval 0.56-0.89; p = 0.004) were found with atopy in Dresden but not in Munich. Neither polymorphism was associated with asthma. Thus, amino acid changes in CX3CR1 may influence the development of atopy but not asthma in German children. Potentially, other factors such as environmental effects may modify the role of CX3CR1 polymorphisms. Copyright (c) 2007 S. Karger AG, Basel
What is Usability? A Characterization based on ISO 9241-11 and ISO/IEC 25010
According to Brooke* "Usability does not exist in any absolute sense; it can
only be defined with reference to particular contexts." That is, one cannot
speak of usability without specifying what that particular usability is
characterized by. Driven by the feedback of a reviewer at an international
conference, I explore in which way one can precisely specify the kind of
usability they are investigating in a given setting. Finally, I come up with a
formalism that defines usability as a quintuple comprising the elements level
of usability metrics, product, users, goals and context of use. Providing
concrete values for these elements then constitutes the investigated type of
usability. The use of this formalism is demonstrated in two case studies.
* J. Brooke. SUS: A "quick and dirty" usability scale. In P. W. Jordan, B.
Thomas, B. A. Weerdmeester, and A. L. McClelland, editors, Usability Evaluation
in Industry. Taylor and Francis, 1996.Comment: Technical Report; Department of Computer Science, Technische
Universit\"at Chemnitz; also available from
https://www.tu-chemnitz.de/informatik/service/ib/2015.php.e
Computing Quantiles in Markov Reward Models
Probabilistic model checking mainly concentrates on techniques for reasoning
about the probabilities of certain path properties or expected values of
certain random variables. For the quantitative system analysis, however, there
is also another type of interesting performance measure, namely quantiles. A
typical quantile query takes as input a lower probability bound p and a
reachability property. The task is then to compute the minimal reward bound r
such that with probability at least p the target set will be reached before the
accumulated reward exceeds r. Quantiles are well-known from mathematical
statistics, but to the best of our knowledge they have not been addressed by
the model checking community so far.
In this paper, we study the complexity of quantile queries for until
properties in discrete-time finite-state Markov decision processes with
non-negative rewards on states. We show that qualitative quantile queries can
be evaluated in polynomial time and present an exponential algorithm for the
evaluation of quantitative quantile queries. For the special case of Markov
chains, we show that quantitative quantile queries can be evaluated in time
polynomial in the size of the chain and the maximum reward.Comment: 17 pages, 1 figure; typo in example correcte
Design of Anisotropic Diffusion Hardware Fiber Phantoms
A gold standard for the validation of diffusion weighted magnetic resonance imaging (DW-MRI) in brain white matter (WM) is essential for clinical purposes but still not available. Synthetic anisotropic fiber bundles are proposed as phantoms for the validation of DW-MRI because of their well-known structure, their long preservability and the possibility
to create complex geometries such as curved and fiber crossings. A crucial question is how the different material properties and size of the fiber phantoms influence the outcome of the DW-MRI experiment. Several fiber materials are compared in this study. The effect of surface
relaxation and internal gradients on the SNR is evaluated. In addition, the dependency of the fiber density and fiber radius on the diffusion properties is investigated
Mutual Unbiasedness in Coarse-grained Continuous Variables
The notion of mutual unbiasedness for coarse-grained measurements of quantum
continuous variable systems is considered. It is shown that while the procedure
of "standard" coarse graining breaks the mutual unbiasedness between conjugate
variables, this desired feature can be theoretically established and
experimentally observed in periodic coarse graining. We illustrate our results
in an optics experiment implementing Fraunhofer diffraction through a periodic
diffraction grating, finding excellent agreement with the derived theory. Our
results are an important step in developing a formal connection between
discrete and continuous variable quantum mechanics.Comment: 5 pages, 3 figures + Supplemental Material (1 page) v2: Introduction
expanded, minor typos correcte
Driven polymer translocation through a nanopore: a manifestation of anomalous diffusion
We study the translocation dynamics of a polymer chain threaded through a
nanopore by an external force. By means of diverse methods (scaling arguments,
fractional calculus and Monte Carlo simulation) we show that the relevant
dynamic variable, the translocated number of segments , displays an {\em
anomalous} diffusive behavior even in the {\em presence} of an external force.
The anomalous dynamics of the translocation process is governed by the same
universal exponent , where is the Flory
exponent and - the surface exponent, which was established recently
for the case of non-driven polymer chain threading through a nanopore. A closed
analytic expression for the probability distribution function , which
follows from the relevant {\em fractional} Fokker - Planck equation, is derived
in terms of the polymer chain length and the applied drag force . It is
found that the average translocation time scales as . Also the corresponding time dependent
statistical moments, and reveal unambiguously the anomalous nature of the translocation
dynamics and permit direct measurement of in experiments. These
findings are tested and found to be in perfect agreement with extensive Monte
Carlo (MC) simulations.Comment: 6 pages, 4 figures, accepted to Europhys. Lett; some references were
supplemented; typos were correcte
Synthesis and (spectro)electrochemistry of mixedvalent diferrocenylâdihydrothiopyran derivatives
Three novel diferrocenyl complexes were prepared and characterised. 2,2-Diferrocenyl-4,5-dimethyl-
3,6-dihydro-2H-thiopyran (1, sulphide) was accessible by the hetero-DielsâAlder reaction of diferrocenyl
thioketone with 2,3-dimethyl-1,3-butadiene. Stepwise oxidation of 1 gave the respective oxides 2,2-
diferrocenyl-4,5-dimethyl-3,6-dihydro-2H-thiopyran-1-oxide (2, sulfoxide) and 2,2-diferrocenyl-4,5-
dimethyl-3,6-dihydro-2H-thiopyran-1,1-dioxide (3, sulfone), respectively. The molecular structures of 1
and 3 in the solid state were determined by single crystal X-ray crystallography. The oxidation of sulphide
1 to sulfone 3, plays only a minor role on the overall structure of the two compounds. Electrochemical
(cyclic voltammetry (= CV), square wave voltammetry (= SWV)) and spectroelectrochemical (in situ
UV-Vis/NIR spectroscopy) studies were carried out. The CV and SWV measurements showed that an
increase of the sulphur atom oxidation from â2 in 1 to +2 in 3 causes an anodic shift of the ferrocenylbased
oxidation potentials of about 100 mV. The electrochemical oxidation of 1â3 generates mixedvalent
cations 1+â3+. These monooxidised species display low-energy electronic absorption bands
between 1000 and 3000 nm assigned to IVCT (= Inter-Valence Charge Transfer) electronic transitions.
Accordingly, the mixed-valent cations 1+â3+ are classified as weakly coupled class II systems according
to Robin and Day.Authors (K. K. and G. M.) thank the National Science Centre
(Poland) for financial support (Project Maestro-3; Dec-2012/06/
A/ST5/00219) and R. C. thanks the German Federal Ministry of
Education and Research (BMBF) for support. The support
from the German Academic Exchange Service (DAAD) in the
framework of the exchange program âOstpartnerschaftenâ is
highly appreciated
Dielectric tensor of monoclinic GaO single crystals in the spectral range eV
The dielectric tensor of -GaO was determined by generalized
spectroscopic ellipsometry in a wide spectral range from to
as well as by calculation including quasiparticle bands and
excitonic effects. The dielectric tensors obtained by both methods are in
excellent agreement with each other and the observed transitions in the
dielectric function are assigned to the corresponding valence bands. It is
shown that the off-diagonal element of the dielectric tensor reaches values up
to and cannot be neglected. Even in the
transparent spectral range where it is quite small () it causes a rotation of the dielectric axes around the symmetry axis of up
to
Self-Consistent Pushing and Cranking Corrections to the Meson Fields of the Chiral Quark-Loop Soliton
We study translational and spin-isospin symmetry restoration for the
two-flavor chiral quark-loop soliton. Instead of a static soliton at rest we
consider a boosted and rotating hedgehog soliton. Corrected classical meson
fields are obtained by minimizing a corrected energy functional which has been
derived by semi-classical methods ('variation after projection'). We evaluate
corrected meson fields in the region 300 MeV \le M \le 600 MeV of constituent
quark masses M and compare them with the uncorrected fields. We study the
effect of the corrections on various expectation values of nuclear observables
such as the root-mean square radius, the axial-vector coupling constant,
magnetic moments and the delta-nucleon mass splitting.Comment: 19 pages, LaTeX, 7 postscript figures included using 'psfig.sty', to
appear in Int.J.Mod.Phys.
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