18,962 research outputs found
Block-Transitive Designs in Affine Spaces
This paper deals with block-transitive - designs in affine
spaces for large , with a focus on the important index case. We
prove that there are no non-trivial 5- designs admitting a
block-transitive group of automorphisms that is of affine type. Moreover, we
show that the corresponding non-existence result holds for 4- designs,
except possibly when the group is one-dimensional affine. Our approach involves
a consideration of the finite 2-homogeneous affine permutation groups.Comment: 10 pages; to appear in: "Designs, Codes and Cryptography
Interplay between nanometer-scale strain variations and externally applied strain in graphene
We present a molecular modeling study analyzing nanometer-scale strain
variations in graphene as a function of externally applied tensile strain. We
consider two different mechanisms that could underlie nanometer-scale strain
variations: static perturbations from lattice imperfections of an underlying
substrate and thermal fluctuations. For both cases we observe a decrease in the
out-of-plane atomic displacements with increasing strain, which is accompanied
by an increase in the in-plane displacements. Reflecting the non-linear elastic
properties of graphene, both trends together yield a non-monotonic variation of
the total displacements with increasing tensile strain. This variation allows
to test the role of nanometer-scale strain variations in limiting the carrier
mobility of high-quality graphene samples
Fluctuation Superconductivity in Mesoscopic Aluminum Rings
Fluctuations are important near phase transitions, where they can be
difficult to describe quantitatively. Superconductivity in mesoscopic rings is
particularly intriguing because the critical temperature is an oscillatory
function of magnetic field. There is an exact theory for thermal fluctuations
in one-dimensional superconducting rings, which are therefore expected to be an
excellent model system. We measure the susceptibility of many rings, one ring
at a time, using a scanning SQUID that can isolate magnetic signals from seven
orders of magnitude larger background applied flux. We find that the
fluctuation theory describes the results and that a single parameter
characterizes the ways in which the fluctuations are especially important at
magnetic fields where the critical temperature is suppressed.Comment: Reprinted with permission from AAA
Superconducting atomic contacts under microwave irradiation
We have measured the effect of microwave irradiation on the dc
current-voltage characteristics of superconducting atomic contacts. The
interaction of the external field with the ac supercurrents leads to replicas
of the supercurrent peak, the well known Shapiro resonances. The observation of
supplementary fractional resonances for contacts containing highly transmitting
conduction channels reveals their non-sinusoidal current-phase relation. The
resonances sit on a background current which is itself deeply modified, as a
result of photon assisted multiple Andreev reflections. The results provide
firm support for the full quantum theory of transport between two
superconductors based on the concept of Andreev bound states
Supply chain management diffusion among firms in the Republic of Ireland
The changing business environment has sharpened the focus on the need for robust approaches to supply chain management (SCM) and the improvement of supply chain capability and performance. This is particularly the case in Ireland, which has the natural disadvantage of a location peripheral to significant markets and sources of raw materials which results in relatively high transport and distribution costs. Therefore, in order to gain insights into current levels of diffusion of SCM, a survey was conducted among 776 firms in the Republic of Ireland. The empirical results suggest that there is a need for more widespread adoption of SCM among Irish firms. This is particularly the case in relation to the four main elements of SCM excellence reported in this paper. The design of supply chain solutions is a highly skilled, knowledge-intensive and complex activity, reflected in a shift from 'box moving' to the design and implementation of customised supply chain solutions. Education and training needs to be addressed by stimulating the development of industry-relevant logistics and SCM resources and skills
Recent developments in radiative B decays
We report on recent theoretical progress in radiative B decays. We focus on a
calculation of logarithmically enhanced QED corrections to the branching ratio
and forward-backward asymmetry in the inclusive rare decay anti-B --> X(s) l+
l-, and present the results of a detailed phenomenological analysis. We also
report on the calculation of NNLO QCD corrections to the inclusive decay anti-B
--> X(s) gamma. As far as exclusive modes are concerned we consider
transversity amplitudes and the impact of right-handed currents in the
exclusive anti-B --> K^* l+ l- decay. Finally, we state results for exclusive B
--> V gamma decays, notably the time-dependent CP-asymmetry in the exclusive B
--> K^* gamma decay and its potential to serve as a so-called ``null test'' of
the Standard Model, and the extraction of CKM and unitarity triangle parameters
from B --> (rho,omega) gamma and B --> K^* gamma decays.Comment: 5 pages, 2 figures. Accepted for publication in the proceedings of
International Europhysics Conference on High Energy Physics (EPS-HEP2007),
Manchester, England, 19-25 Jul 200
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