6,816 research outputs found
Requirement of Pax6 for the integration of guidance cues in cell migration
Data accessibility. Cell trajectories data and a summary of directedness and angle values are deposited at Dryad: http://dx.doi.org/10.5061/dryad.53512. Funding MA was funded by an Alban International Research Studentship (code: E07D400602UY).Peer reviewedPublisher PD
A complete criterion for separability detection
Using new results on the separability properties of bosonic systems, we
provide a new complete criterion for separability. This criterion aims at
characterizing the set of separable states from the inside by means of a
sequence of efficiently solvable semidefinite programs. We apply this method to
derive arbitrarily good approximations to the optimal measure-and-prepare
strategy in generic state estimation problems. Finally, we report its
performance in combination with the criterion developed by Doherty et al. [1]
for the calculation of the entanglement robustness of a relevant family of
quantum states whose separability properties were unknown
Band selection and disentanglement using maximally-localized Wannier functions: the cases of Co impurities in bulk copper and the Cu (111) surface
We have adapted the maximally-localized Wannier function approach of [I.
Souza, N. Marzari and D. Vanderbilt, Phys. Rev. B 65, 035109 (2002)] to the
density functional theory based Siesta method [J. M. Soler et al., J. Phys.:
Cond. Mat. 14, 2745 (2002)] and applied it to the study of Co substitutional
impurities in bulk copper as well as to the Cu (111) surface. In the Co
impurity case, we have reduced the problem to the Co d-electrons and the Cu
sp-band, permitting us to obtain an Anderson-like Hamiltonian from well defined
density functional parameters in a fully orthonormal basis set. In order to
test the quality of the Wannier approach to surfaces, we have studied the
electronic structure of the Cu (111) surface by again transforming the density
functional problem into the Wannier representation. An excellent description of
the Shockley surface state is attained, permitting us to be confident in the
application of this method to future studies of magnetic adsorbates in the
presence of an extended surface state
Thermal profiles within the channel of planar gunn diodes using micro-particle sensors
The paper describes the use of a novel microparticle sensor (~3 μm diameter) and infra-red (IR) microscopy to measure the temperature profile within the active channel (typically 3 μm length and 120 μm width) of planar Gunn diodes. The method has enabled detailed temperature measurements showing an asymmetrical temperature profile along the active width of these devices. The asymmetrical temperature profile suggests a similar behaviour in the channel current density, which may contribute to the lower than expected RF output power
Leptonic universality breaking in Upsilon decays as a probe of new physics
In this work we examine the possible existence of new physics beyond the
standard model which could modify the branching fractions of the leptonic
(mainly tauonic) decays of bottomonium vector resonances below the
threshold. The decay width is factorized as the product of two pieces: a) the
probability of an intermediate pseudoscalar color-singlet state
(coupling to the dominant Fock state of the Upsilon via a magnetic dipole
transition) and a soft (undetected) photon; b) the annihilation width of the
pair into two leptons, mediated by a non-standard CP-odd Higgs boson
of mass about 10 GeV, introducing a quadratic dependence on the lepton mass in
the partial width. The process would be unwittingly ascribed to the
leptonic channel thereby (slightly) breaking lepton universality. A possible
mixing of the pseudoscalar Higgs and bottomonium resonances is also considered.
Finally, several experimental signatures to check out the validity of the
conjecture are discussed.Comment: LaTeX, 22 pages, 2 EPS figure
The accretion environment in Vela X-1 during a flaring period using XMM-Newton
We present analysis of 100 ks contiguous XMM-Newton data of the prototypical
wind accretor Vela X-1. The observation covered eclipse egress between orbital
phases 0.134 and 0.265, during which a giant flare took place, enabling us to
study the spectral properties both outside and during the flare. This giant
flare with a peak luminosity of erg
s allows estimates of the physical parameters of the accreted structure
with a mass of g.
We have been able to model several contributions to the observed spectrum
with a phenomenological model formed by three absorbed power laws plus three
emission lines. After analysing the variations with orbital phase of the column
density of each component, as well as those in the Fe and Ni fluorescence
lines, we provide a physical interpretation for each spectral component.
Meanwhile, the first two components are two aspects of the principal accretion
component from the surface of the neutron star, and the third component seems
to be the \textit{X-ray light echo} formed in the stellar wind of the
companion.Comment: Accepted. Astronomy and Astrophysics, 201
Quantum Spins and Quasiperiodicity: a real space renormalization group approach
We study the antiferromagnetic spin-1/2 Heisenberg model on a two-dimensional
bipartite quasiperiodic structure, the octagonal tiling -- the aperiodic
equivalent of the square lattice for periodic systems.
An approximate block spin renormalization scheme is described for this
problem. The ground state energy and local staggered magnetizations for this
system are calculated, and compared with the results of a recent Quantum Monte
Carlo calculation for the tiling. It is conjectured that the ground state
energy is exactly equal to that of the quantum antiferromagnet on the square
lattice.Comment: To appear in Physical Review Letter
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