26 research outputs found
An extension of Laplace's method
Asymptotic expansions are obtained for contour integrals of the form in which
is a large real or complex parameter, , and are
analytic functions of , and the positive constants and are
related to the local behaviour of the functions and near the
endpoint . Our main theorem includes as special cases several important
asymptotic methods for integrals such as those of Laplace, Watson, Erd\'elyi
and Olver. Asymptotic expansions similar to ours were derived earlier by Dingle
using formal, non-rigorous methods. The results of the paper also serve to
place Dingle's investigations on a rigorous mathematical foundation. The new
results have potential applications in the asymptotic theory of special
functions in transition regions, and we illustrate this by two examples.Comment: 19 pages, 2 figures, revised version, accepted for publication in
Constructive Approximatio
Magnetic and transport properties in ordered arrays of permalloy antidots and thin films
The magnetotransport behaviors of two types of permalloy nanostructures, thin films and antidots, are presented and discussed. Antidots samples were prepared by sputtering a Ni(80)Fe(20) layer on top of a nanoporous alumina membrane. A counterpart continuous thin film grown on a continuous Si substrate was also prepared. The magnetoresistance (MR) was measured both as a function of the external applied magnetic field and of the angular orientation, and thus compared with the magnetization curves. The introduction of antidots is found to reduce the anisotropic MR and the angular dependence of the MR, simultaneously increasing the coercive field of the samples. The influence of the sample geometry on the perpendicular MR behavior is reported and discussed. (C) 2010 American Institute of Physics. [doi:10.1063/1.3383039]107
Human newborn bacille Calmette–Guérin vaccination and risk of tuberculosis disease: a case-control study
: An incomplete understanding of the immunological mechanisms underlying protection against tuberculosis (TB) hampers the development of new vaccines against TB. We aimed to define host correlates of prospective risk of TB disease following bacille Calmette-Guérin (BCG) vaccination. : In this study, 5,726 infants vaccinated with BCG at birth were enrolled. Host responses in blood collected at 10 weeks of age were compared between infants who developed pulmonary TB disease during 2 years of follow-up (cases) and those who remained healthy (controls). : Comprehensive gene expression and cellular and soluble marker analysis failed to identify a correlate of risk. We showed that distinct host responses after BCG vaccination may be the reason: two major clusters of gene expression, with different myeloid and lymphoid activation and inflammatory patterns, were evident when all infants were examined together. Cases from each cluster demonstrated distinct patterns of gene expression, which were confirmed by cellular assays. : Distinct patterns of host responses to Mycobacterium bovis BCG suggest that novel TB vaccines may also elicit distinct patterns of host responses. This diversity should be considered in future TB vaccine development
Large tunable valley splitting in edge-free graphene quantum dots on boron nitride
Coherent manipulation of binary degrees of freedom is at the heart of modern
quantum technologies. Graphene offers two binary degrees: the electron spin and
the valley. Efficient spin control has been demonstrated in many solid state
systems, while exploitation of the valley has only recently been started, yet
without control on the single electron level. Here, we show that van-der Waals
stacking of graphene onto hexagonal boron nitride offers a natural platform for
valley control. We use a graphene quantum dot induced by the tip of a scanning
tunneling microscope and demonstrate valley splitting that is tunable from -5
to +10 meV (including valley inversion) by sub-10-nm displacements of the
quantum dot position. This boosts the range of controlled valley splitting by
about one order of magnitude. The tunable inversion of spin and valley states
should enable coherent superposition of these degrees of freedom as a first
step towards graphene-based qubits
Control of magnetic anisotropy by orbital hybridization in (La0.67Sr0.33MnO3)n/(SrTiO3)n superlattice
The asymmetry of chemical nature at the hetero-structural interface offers an
unique opportunity to design desirable electronic structure by controlling
charge transfer and orbital hybridization across the interface. However, the
control of hetero-interface remains a daunting task. Here, we report the
modulation of interfacial coupling of (La0.67Sr0.33MnO3)n/(SrTiO3)n
superlattices by manipulating the periodic thickness with n unit cells of
SrTiO3 and n unit cells La0.67Sr0.33MnO3. The easy axis of magnetic anisotropy
rotates from in-plane (n = 10) to out-of-plane (n = 2) orientation at 150 K.
Transmission electron microscopy reveals enlarged tetragonal ratio > 1 with
breaking of volume conservation around the (La0.67Sr0.33MnO3)n/(SrTiO3)n
interface, and electronic charge transfer from Mn to Ti 3d orbitals across the
interface. Orbital hybridization accompanying the charge transfer results in
preferred occupancy of 3d3z2-r2 orbital at the interface, which induces a
stronger electronic hopping integral along the out-of-plane direction and
corresponding out-of-plane magnetic easy axis for n = 2. We demonstrate that
interfacial orbital hybridization in superlattices of strongly correlated
oxides may be a promising approach to tailor electronic and magnetic properties
in device applications
CMR-determined scar volume: predictive for ventricular tachycardias?
The interesting data reported by Bernhardt et al. strengthen the diagnostic benefit of CMR in patients with ischemic cardiomyopathy. Consequently, the presence, location and size of the CMR-determined scar tissue may be used for better risk stratification in patients with ischemic cardiomyopathy eligible for ICD therapy