181 research outputs found
Dopant-Dopant Interactions in Beryllium doped Indium Gallium Arsenide: an Ab Initio Study
We present an ab initio study of dopant-dopant interactions in
beryllium-doped InGaAs. We consider defect formation energies of various
interstitial and substitutional defects and their combinations. We find that
all substitutional-substitutional interactions can be neglected. On the other
hand, interactions involving an interstitial defect are significant. Specially,
interstitial Be is stabilized by about 0.9/1.0 eV in the presence of one/two
BeGa substitutionals. Ga interstitial is also substantially stabilized by Be
interstitials. Two Be interstitials can form a metastable Be-Be-Ga complex with
a dissociation energy of 0.26 eV/Be. Therefore, interstitial defects and
defect-defect interactions should be considered in accurate models of Be doped
InGaAs. We suggest that In and Ga should be treated as separate atoms and not
lumped into a single effective group III element, as has been done before. We
identified dopant-centred states which indicate the presence of other charge
states at finite temperatures, specifically, the presence of Beint+1 (as
opposed to Beint+2 at 0K)
The Csk-binding protein PAG regulates PDGF-induced Src mitogenic signaling via GM1
Spatial regulation is an important feature of signal specificity elicited by cytoplasmic tyrosine kinases of the Src family (SRC family protein tyrosine kinases [SFK]). Cholesterol-enriched membrane domains, such as caveolae, regulate association of SFK with the platelet-derived growth factor receptor (PDGFR), which is needed for kinase activation and mitogenic signaling. PAG, a ubiquitously expressed member of the transmembrane adaptor protein family, is known to negatively regulate SFK signaling though binding to Csk. We report that PAG modulates PDGFR levels in caveolae and SFK mitogenic signaling through a Csk-independent mechanism. Regulation of SFK mitogenic activity by PAG requires the first N-terminal 97 aa (PAG-N), which include the extracellular and transmembrane domains, palmitoylation sites, and a short cytoplasmic sequence. We also show that PAG-N increases ganglioside GM1 levels at the cell surface and, thus, displaces PDGFR from caveolae, a process that requires the ganglioside-specific sialidase Neu-3. In conclusion, PAG regulates PDGFR membrane partitioning and SFK mitogenic signaling by modulating GM1 levels within caveolae independently from Csk
Magnetoconductance Oscillations in Ballistic Semiconductor-Superconductor Junctions
The mechanism of the magnetoconductance oscillations in junctions of a
ballistic semiconductor and a superconductor is discussed. The oscillations
appear when both the normal and the Andreev reflection occur at the interface.
The interplay between the classical cyclotron motion of a quasiparticle and the
phase shift caused by the magnetic field is the origin of the conductance
oscillations.Comment: 4 pages, 4 figure
Validation of the oxygen desaturation index in the diagnostic workup of obstructive sleep apnea
Introduction: Obstructive sleep apnea (OSA) is common, and diagnosis requires expensive and laborious testing to assess the apnea hypopnea index (AHI). We performed an analysis to explore the relationship between the oxygen desaturation index (ODI) as measured with pulse oximetry and the AHI in our large portable monitoring (PM) database to find an optimal cutoff value for the ODI in order to be able to exclude AHI ≥ 5 on PM. Methods: Three thousand four hundred thirteen PM recordings were randomly divided into a training set (N = 2281) and a test set (N = 1132). The optimal cutoff for the ODI to exclude an AHI ≥ 5 on PM was determined in the training set and subsequently validated in the test set. Results: Area under the curve of the ODI to exclude an AHI ≥ 5 on PM was 0.997 in the training set and 0.996 in the test set. In the training set, the optimal cutoff to predict an AHI < 5 was an ODI < 5. Using this cutoff in the test set provided a sensitivity of 97.7%, a specificity of 97.0%, a positive predictive value of 99.2%, and a negative predictive value of 91.4%. Conclusion: An ODI < 5 predicts an AHI < 5 with high sensitivity and specificity when measured simultaneously using the same oximeter during PM recording
Reflectionless tunneling in ballistic normal-metal--superconductor junctions
We investigate the phenomenon of reflectionless tunneling in ballistic
normal-metal--superconductor (NS) structures, using a semiclassical formalism.
It is shown that applied magnetic field and superconducting phase difference
both impair the constructive interference leading to this effect, but in a
qualitatively different way. This is manifested both in the conductance and in
the shot noise properties of the system considered. Unlike diffusive systems,
the features of the conductance are sharp, and enable fine spatial control of
the current, as well as single channel manipulations. We discuss the
possibility of conducting experiments in ballistic semiconductor-superconductor
structures with smooth interfaces and some of the phenomena, specific to such
structures, that could be measured. A general criterion for the barrier at NS
interfaces, though large, to be effectively transparent to pair current is
obtained.Comment: published versio
Angle dependence of Andreev scattering at semiconductor-superconductor interfaces
We study the angle dependence of the Andreev scattering at a
semiconductor-superconductor interface, generalizing the one-dimensional theory
of Blonder, Tinkham and Klapwijk. An increase of the momentum parallel to the
interface leads to suppression of the probability of Andreev reflection and
increase of the probability of normal reflection. We show that in the presence
of a Fermi velocity mismatch between the semiconductor and the superconductor
the angles of incidence and transmission are related according to the
well-known Snell's law in optics. As a consequence there is a critical angle of
incidence above which only normal reflection exists. For two and
three-dimensional interfaces a lower excess current compared to ballistic
transport with perpendicular incidence is found. Thus, the one-dimensional BTK
model overestimates the barrier strength for two and three-dimensional
interfaces.Comment: 8 pages including 3 figures (revised, 6 references added
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