2,306 research outputs found
Study of double exposure holography of the 3-dimensional character of the flow around an airfoil profile in a wind tunnel
The tridimensional character of the flow around a profile placed between walls is demonstrated and the incidence induced with the assistance of measurements of velocities by double exposure holography is evaluated. The values obtained by the theory of Menard are compared satisfactorily to the values obtained by this experiment
Haplotype reconstruction error as a classical misclassification problem
Statistically reconstructing haplotypes from single nucleotide polymorphism (SNP) genotypes, can lead to falsely classified haplotypes. This can be an issue when interpreting haplotype association results or when selecting subjects with certain haplotypes for subsequent functional studies. It was our aim to quantify haplotype reconstruction error and to provide tools for it.
By numerous simulation scenarios, we systematically investigated several error measures, including discrepancy, error rate, and R(2), and introduced the sensitivity and specificity to this context. We exemplified several measures in the KORA study, a large population-based study from Southern Germany. We find that the specificity is slightly reduced only for common haplotypes, while the sensitivity was decreased for some, but not all rare haplotypes. The overall error rate was generally increasing with increasing number of loci, increasing minor allele frequency of SNPs, decreasing correlation between the alleles and increasing ambiguity.
We conclude that, with the analytical approach presented here, haplotype-specific error measures can be computed to gain insight into the haplotype uncertainty. This method provides the information, if a specific risk haplotype can be expected to be reconstructed with rather no or high misclassification and thus on the magnitude of expected bias in association estimates. We also illustrate that sensitivity and specificity separate two dimensions of the haplotype reconstruction error, which completely describe the misclassification matrix and thus provide the prerequisite for methods accounting for misclassification
Migration, trade and unemployment
A source of anxiety of policy makers and the public in general is the detrimental impact of trade and immigration on unemployment. The transitory restrictions for worker migration after the EU enlargements of 2004 and 2007 exemplify the supposed negative effect of immigration on labor markets. This paper aims to identify the effects of immigration alongside trade on unemployment controlling for the high correlation between immigration and goods flows in order to prevent an omitted variable bias. The authors use data from 24 OECD countries over the period from 1997 to 2007 and employ instrumental variables fixed effects and dynamic panel estimators in order to account for unobserved heterogeneity as well as the potential endogeneity of migration flows and the high persistence of unemployment. We find no significant effect of immigration on unemployment on average.Benedikt Heid, Mario Larc
Phonon dispersion and electron-phonon coupling in MgB_2 and AlB_2
We present a first principles investigation of the lattice dynamics and
electron-phonon coupling of the superconductor MgB_2 and the isostructural
AlB_2 within the framework of density functional perturbation theory using a
mixed-basis pseudopotential method. Complete phonon dispersion curves and
Eliashberg functions \alpha^2F are calculated for both systems. We also report
on Raman measurements, which support the theoretical findings. The calculated
generalized density-of-states for MgB_2 is in excellent agreement with recent
neutron-scattering experiments. The main differences in the calculated phonon
spectra and \alpha^2F are related to high frequency in-plane boron vibrations.
As compared to AlB_2, they are strongly softened in MgB_2 and exhibit an
exceptionally strong coupling to electronic states at the Fermi energy. The
total coupling constants are \lambda_{MgB_2}=0.73 and \lambda_{AlB_2}=0.43.
Implications for the superconducting transition temperature are briefly
discussed.Comment: 10 pages, 4 figures, to appear in Phys. Rev. Let
Spatial exporters
In this paper, we provide causal evidence that firms serve new markets which are geographically close to their prior export destinations with a higher probability than standard gravity models predict. We quantify the impact of this spatial pattern using a data set of Chinese firms which had never exported to the EU, the United States, and Canada before 2005. These countries imposed import quotas on textile and apparel products until 2005 and experienced a subsequent increase in imports of previously constrained Chinese firms. Controlling for firm-destination specific effects and accounting for potential true state dependence we show that the probability to export to a country increases by about two percentage points for each prior export destination which shares a common border with this country. We find little evidence for other forms of proximity to previous export destinations like common colonizer, language or income group
Security of coherent state quantum cryptography in the presence of Gaussian noise
We investigate the security against collective attacks of a continuous
variable quantum key distribution scheme in the asymptotic key limit for a
realistic setting. The quantum channel connecting the two honest parties is
assumed to be lossy and imposes Gaussian noise on the observed quadrature
distributions. Secret key rates are given for direct and reverse reconciliation
schemes including postselection in the collective attack scenario. The effect
of a non-ideal error correction and two-way communication in the classical
post-processing step is also taken into account.Comment: 12 pages, 5 figures updated version including two-way communication;
changed the definition of the excess noise to match the definition given
earlier (Phys. Rev. Lett. 92, 117901); submitted to PRA; presented at the 8th
International Conference on Quantum Communication, Measurement and Computing,
Tsukub
Ab initio lattice dynamics and electron-phonon coupling of Bi(111)
We present a comprehensive ab initio study of structural, electronic, lattice
dynamical and electron-phonon coupling properties of the Bi(111) surface within
density functional perturbation theory. Relativistic corrections due to
spin-orbit coupling are consistently taken into account. As calculations are
carried out in a periodic slab geometry, special attention is given to the
convergence with respect to the slab thickness. Although the electronic
structure of Bi(111) thin films varies significantly with thickness, we found
that the lattice dynamics of Bi(111) is quite robust and appears converged
already for slabs as thin as 6 bilayers. Changes of interatomic couplings are
confined mostly to the first two bilayers, resulting in super-bulk modes with
frequencies higher than the optic bulk spectrum, and in an enhanced density of
states at lower frequencies for atoms in the first bilayer. Electronic states
of the surface band related to the outer part of the hole Fermi surfaces
exhibit a moderate electron-phonon coupling of about 0.45, which is larger than
the coupling constant of bulk Bi. States at the inner part of the hole surface
as well as those forming the electron pocket close to the zone center show much
increased couplings due to transitions into bulk projected states near
Gamma_bar. For these cases, the state dependent Eliashberg functions exhibit
pronounced peaks at low energy and strongly deviate in shape from a Debye-like
spectrum, indicating that an extraction of the coupling strength from measured
electronic self-energies based on this simple model is likely to fail.Comment: 30 pages, 11 figure
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