3,514 research outputs found
Optical alignment and polarization conversion of neutral exciton spin in individual InAs/GaAs quantum dots
We investigate exciton spin memory in individual InAs/GaAs self-assembled
quantum dots via optical alignment and conversion of exciton polarization in a
magnetic field. Quasiresonant phonon-assisted excitation is successfully
employed to define the initial spin polarization of neutral excitons. The
conservation of the linear polarization generated along the bright exciton
eigenaxes of up to 90% and the conversion from circular- to linear polarization
of up to 47% both demonstrate a very long spin relaxation time with respect to
the radiative lifetime. Results are quantitatively compared with a model of
pseudo-spin 1/2 including heavy-to-light hole mixing.Comment: 5 pages, 3 figure
Anisotropic magneto-resistance in a GaMnAs-based single impurity tunnel diode: a tight binding approach
Using an advanced tight-binding approach, we estimate the anisotropy of the
tunnel transmission associated with the rotation of the 5/2 spin of a single Mn
atom forming an acceptor state in GaAs and located near an AlGaAs tunnel
barrier. Significant anisotropies in both in-plane and out-of-plane geometries
are found, resulting from the combination of the large spin-orbit coupling
associated with the p-d exchange interaction, cubic anisotropy of heavy-hole
dispersion and the low C2v symmetry of the chemical bonds.Comment: 4 pages, 3 figure
Study of the general mechanism of stress corrosion of aluminum alloys and development of techniques for its detection Quarterly report, 1 Dec. 1967 - 29 Feb. 1968
Stress corrosion of aluminum alloys and techniques for its detectio
Optically probing the fine structure of a single Mn atom in an InAs quantum dot
We report on the optical spectroscopy of a single InAs/GaAs quantum dot (QD)
doped with a single Mn atom in a longitudinal magnetic field of a few Tesla.
Our findings show that the Mn impurity is a neutral acceptor state A^0 whose
effective spin J=1 is significantly perturbed by the QD potential and its
associated strain field. The spin interaction with photo-carriers injected in
the quantum dot is shown to be ferromagnetic for holes, with an effective
coupling constant of a few hundreds of micro-eV, but vanishingly small for
electrons.Comment: 5 pages, 3 figure
Study of the general mechanism of stress corrosion of aluminum alloys and development of techniques for its detection Annual summary report, 2 Jun. 1967 - 1 Jun. 1968
Stress corrosion cracking of high strength aluminum alloys investigated by electrochemical, mechanical, and electron microscopic technique
Electronic states and optical properties of GaAs/AlAs and GaAs/vacuum superlattices by the linear combination of bulk bands method
The linear combination of bulk bands method recently introduced by Wang,
Franceschetti and Zunger [Phys. Rev. Lett.78, 2819 (1997)] is applied to a
calculation of energy bands and optical constants of (GaAs)/(AlAs) and
(GaAs)/(vacuum) (001) superlattices with n ranging from 4 to 20.
Empirical pseudopotentials are used for the calculation of the bulk energy
bands. Quantum-confined induced shifts of critical point energies are
calculated and are found to be larger for the GaAs/vacuum system. The
peak in the absorption spectra has a blue shift and splits into two peaks for
decreasing superlattice period; the transition instead is found to be
split for large-period GaAs/AlAs superlattices. The band contribution to linear
birefringence of GaAs/AlAs superlattices is calculated and compared with recent
experimental results of Sirenko et al. [Phys. Rev. B 60, 8253 (1999)]. The
frequency-dependent part reproduces the observed increase with decreasing
superlattice period, while the calculated zero-frequency birefringence does not
account for the experimental results and points to the importance of
local-field effects.Comment: 10 pages, 11 .eps figures, 1 tabl
Spin-orbit coupling and intrinsic spin mixing in quantum dots
Spin-orbit coupling effects are studied in quantum dots in InSb, a narrow-gap
material. Competition between different Rashba and Dresselhaus terms is shown
to produce wholesale changes in the spectrum. The large (and negative)
-factor and the Rashba field produce states where spin is no longer a good
quantum number and intrinsic flips occur at moderate magnetic fields. For dots
with two electrons, a singlet-triplet mixing occurs in the ground state, with
observable signatures in intraband FIR absorption, and possible importance in
quantum computation.Comment: REVTEX4 text with 3 figures (high resolution figs available by
request). Submitted to PR
Increased myeloid cell hypoxia-inducible factor-1 delays obliterative airway disease in the mouse
BACKGROUND: Obliterative bronchiolitis after lung transplantation is characterized by chronic airway inflammation leading to the obliteration of small airways. Hypoxia-inducible factor-1 (HIF-1) is a master regulator of cellular responses to hypoxia and inflammation. The Von Hippel-Lindau protein (pVHL) drives the degradation of oxygen-sensitive subunit HIF-1 alpha that controls the activity of HIF-1. We investigated the effect of myeloid cell targeted gene deletion of HIF-1 alpha or its negative regulator pVHL on the development of obliterative airway disease (OAD) in the recipients of tracheal allografts, a mouse model for obliterative bronchiolitis after lung transplantation. METHODS: Tracheal allografts were heterotopically transplanted from BALB/c donor mice to fully major histocompatibility complex mismatched recipient mice with HIF-1 alpha or VHL gene deletion in myeloid cells. The recipients were left non-immunosuppressed or received tacrolimus daily. Histologic, immunohistochemical, and real-time reverse transcription polymerase chain reaction analyses were performed at 3, 10, and 30 days. RESULTS: In the absence of immunosuppression, myeloid cell-specific VHL deficiency of the recipient mice improved epithelial recovery, decreased inflammatory cell infiltration and expression of pro-inflammatory cytokines, increased regulatory forkhead box P3 messenger RNA expression, and reduced OAD development in tracheal allografts. In the presence of tacrolimus immunosuppression, loss of HIF-1 alpha activity in myeloid cells of the recipient by HIF-1 alpha gene deletion accelerated OAD development in mouse tracheal allografts. CONCLUSIONS: Activity of the HIF-pathway affects the development of allograft rejection, and our results suggest that myeloid cell-specific VHL-deficiency that potentially increases HIF-activity decreases allograft inflammation and the subsequent development of OAD in mouse tracheal allografts. (C) 2016 International Society for Heart and Lung Transplantation. All rights reserved.Peer reviewe
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