4,713 research outputs found
Ion-Exchanged Glass Waveguides with Low Birefringence for a Broad Range of Waveguide Widths
Optical communications networks require integrated photonic components with negligible polarization dependence, which typically means that the waveguides must feature very low birefringence. Recent studies have shown that waveguides with low birefringence can be obtained, e.g., by use of silica-on-silicon waveguides or buried ion-exchanged glass waveguides. However, many integrated photonic circuits consist of waveguides with varying widths. Therefore low birefringence is consequently required for waveguides having different widths. This is a difficult task for most waveguide fabrication technologies. We present experimental results on waveguide birefringence for buried silverâsodium ion-exchanged glass waveguides. We show that the waveguide birefringence of the order of 106 for waveguide mask opening widths ranging from 2 to 10 ÎŒm can be obtained by postprocessing the sample through annealing at an elevated temperature. The measured values are in agreement with the values calculated with our modeling software for ion-exchanged glass waveguides. This unique feature of ion-exchanged waveguides may be of significant importance in a wide variety of integrated photonic circuits requiring polarization independent operation
A view from inside iron-based superconductors
Muon spin spectroscopy is one of the most powerful tools to investigate the
microscopic properties of superconductors. In this manuscript, an overview on
some of the main achievements obtained by this technique in the iron-based
superconductors (IBS) are presented. It is shown how the muons allow to probe
the whole phase diagram of IBS, from the magnetic to the superconducting phase,
and their sensitivity to unravel the modifications of the magnetic and the
superconducting order parameters, as the phase diagram is spanned either by
charge doping, by an external pressure or by introducing magnetic and
non-magnetic impurities. Moreover, it is highlighted that the muons are unique
probes for the study of the nanoscopic coexistence between magnetism and
superconductivity taking place at the crossover between the two ground-states.Comment: 28 pages, 18 figure
Prior Experience and Export Performance: The Missing Link of Global Vision
Despite the scholarly interest in the prior experience of entrepreneurs expressed by the field of International Entrepreneurship, empirical investigation linking prior experience with international performance leads to inconclusive and conflicting results. Based on the concept of human capital and resource-based theory, this study provides a supplementary explanation by integrating global vision âthe cognitive capital of the entrepreneur related to an international orientationâ into this relationship. The study hypothesises that there is no direct relationship between entrepreneursâ prior experience and export performance; rather, this relationship is mediated by an entrepreneurâs global vision. The hypotheses were tested using structural equation modelling, drawing on a sample of 332 early internationalising SMEs in Bangladesh. To overcome the cognitive inertia resulting from prior experiences, entrepreneurs must focus on their cognitive capabilities, in particular the ability to see the world through a global lens. In order to improve export performance, policymakers must also provide additional support to strengthen entrepreneursâ global vision
A study on subarcsecond scales of the ammonia and continuum emission toward the G16.59-0.05 high-mass star-forming region
We wish to investigate the structure, velocity field, and stellar content of
the G16.59-0.05 high-mass star-forming region, where previous studies have
established the presence of two almost perpendicular (NE-SW and SE-NW), massive
outflows, and a rotating disk traced by methanol maser emission. We performed
Very Large Array observations of the radio continuum and ammonia line emission,
complemented by COMICS/Subaru and Hi-GAL/Herschel images in the mid- and
far-infrared (IR). Our centimeter continuum maps reveal a collimated radio jet
that is oriented E-W and centered on the methanol maser disk, placed at the SE
border of a compact molecular core. The spectral index of the jet is negative,
indicating non-thermal emission over most of the jet, except the peak close to
the maser disk, where thermal free-free emission is observed. We find that the
ammonia emission presents a bipolar structure consistent (on a smaller scale)
in direction and velocity with that of the NE-SW bipolar outflow detected in
previous CO observations. After analyzing our previous N2H+(1-0) observations
again, we conclude that two scenarios are possible. In one case both the radio
jet and the ammonia emission would trace the root of the large-scale CO bipolar
outflow. The different orientation of the jet and the ammonia flow could be
explained by precession and/or a non-isotropic density distribution around the
star. In the other case, the N2H+(1-0) and ammonia bipolarity is interpreted as
two overlapping clumps moving with different velocities along the line of
sight. The ammonia gas also seems to undergo rotation consistent with the maser
disk. Our IR images complemented by archival data allow us to derive a
bolometric luminosity of about 10^4 L_sun and to conclude that most of the
luminosity is due to the young stellar object associated with the maser disk.Comment: 11 pages, 12 figures, published in Astronomy and Astrophysic
Evidence for impurity-induced frustration in La2CuO4
Zero-field muon spin rotation and magnetization measurements were performed
in La2Cu{1-x}MxO4, for 0<x< 0.12, where Cu2+ is replaced either by M=Zn2+ or by
M=Mg2+ spinless impurity. It is shown that while the doping dependence of the
sublattice magnetization (M(x)) is nearly the same for both compounds, the
N\'eel temperature (T_N(x)) decreases unambiguously more rapidly in the
Zn-doped compound. This difference, not taken into account within a simple
dilution model, is associated with the frustration induced by the Zn2+ impurity
onto the Cu2+ antiferromagnetic lattice. In fact, from T_N(x) and M(x) the spin
stiffness is derived and found to be reduced by Zn doping more significantly
than expected within a dilution model. The effect of the structural
modifications induced by doping on the exchange coupling is also discussed.Comment: 4 pages, 4 figure
Critical chain length and superconductivity emergence in oxygen-equalized pairs of YBa2Cu3O6.30
The oxygen-order dependent emergence of superconductivity in YBa2Cu3O6+x is
studied, for the first time in a comparative way, on pair samples having the
same oxygen content and thermal history, but different Cu(1)Ox chain
arrangements deriving from their intercalated and deintercalated nature.
Structural and electronic non-equivalence of pairs samples is detected in the
critical region and found to be related, on microscopic scale, to a different
average chain length, which, on being experimentally determined by nuclear
quadrupole resonance (NQR), sheds new light on the concept of critical chain
length for hole doping efficiency.Comment: 7 RevTex pages, 2 Postscript figures. Submitted to Phys. Rev.
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