134 research outputs found
Determination of the absolute internal quantum efficiency of photoluminescence in GaN co-doped with Si and Zn
The optical properties of high-quality GaN co-doped with silicon and zinc are investigated by using temperature-dependent continuous-wave and time-resolved photoluminescence measurements. The blue luminescence band is related to the ZnGa acceptor in GaN:Si,Zn, which exhibits an exceptionally high absolute internal quantum efficiency (IQE). An IQE above 90% was calculated for several samples having different concentrations of Zn. Accurate and reliable values of the IQE were obtained by using several approaches based on rate equations. The concentrations of the ZnGa acceptors and free electrons were also estimated from the photoluminescence measurements
Liveâvirtualâconstructive simulation for testing and evaluation of air combat tactics, techniques, and procedures, Part 1: assessment framework
Spin diffusion in the Mn2+ ion system of II-VI diluted magnetic semiconductor heterostructures
The magnetization dynamics in diluted magnetic semiconductor heterostructures
based on (Zn,Mn)Se and (Cd,Mn)Te has been studied experimentally by optical
methods and simulated numerically. In the samples with nonhomogeneous magnetic
ion distribution this dynamics is contributed by spin-lattice relaxation and
spin diffusion in the Mn spin system. The spin diffusion coefficient of
7x10^(-8) cm^2/s has been evaluated for Zn(0.99)Mn(0.01)Se from comparison of
experimental and numerical results. Calculations of the giant Zeeman splitting
of the exciton states and the magnetization dynamics in the ordered alloys and
parabolic quantum wells fabricated by the digital growth technique show perfect
agreement with the experimental data. In both structure types the spin
diffusion has an essential contribution to the magnetization dynamics.Comment: 12 pages, 11 figure
Electron cyclotron mass in undoped CdTe/CdMnTe quantum wells
Optically detected cyclotron resonance of two-dimensional electrons has been
studied in nominally undoped CdTe/(Cd,Mn)Te quantum wells. The enhancement of
carrier quantum confinement results in an increase of the electron cyclotron
mass from 0.099 to 0.112 with well width decreasing from 30 down to
3.6 nm. Model calculations of the electron effective mass have been performed
for this material system and good agreement with experimental data is achieved
for an electron-phonon coupling constant =0.32
The band structure of BeTe - a combined experimental and theoretical study
Using angle-resolved synchrotron-radiation photoemission spectroscopy we have
determined the dispersion of the valence bands of BeTe(100) along ,
i.e. the [100] direction. The measurements are analyzed with the aid of a
first-principles calculation of the BeTe bulk band structure as well as of the
photoemission peaks as given by the momentum conserving bulk transitions.
Taking the calculated unoccupied bands as final states of the photoemission
process, we obtain an excellent agreement between experimental and calculated
spectra and a clear interpretation of almost all measured bands. In contrast,
the free electron approximation for the final states fails to describe the BeTe
bulk band structure along properly.Comment: 21 pages plus 4 figure
Epitaxy and Magneto-transport properties of the diluted magnetic semiconductor p- Be(1-x)MnxTe
We report on the MBE-growth and magnetotransport properties of p-type BeMnTe,
a new ferromagnetic diluted magnetic semiconductor. BeMnTe thin film structures
can be grown almost lattice matched to GaAs for Mn concentrations up to 10%
using solid source MBE. A high p-type doping with nitrogen can be achieved by
using an RF-plasma source. BeMnTe and BeTe layers have been characterized by
magneto-transport measurements. At low temperatures, the BeMnTe samples exhibit
a large anomalous Hall effect. A hysteresis in the anomalous Hall effect
appears below 2.5K in the most heavily doped sample, which indicates the
occurrence of a ferromagnetic phase.Comment: pdf onl
Spintronics: Fundamentals and applications
Spintronics, or spin electronics, involves the study of active control and
manipulation of spin degrees of freedom in solid-state systems. This article
reviews the current status of this subject, including both recent advances and
well-established results. The primary focus is on the basic physical principles
underlying the generation of carrier spin polarization, spin dynamics, and
spin-polarized transport in semiconductors and metals. Spin transport differs
from charge transport in that spin is a nonconserved quantity in solids due to
spin-orbit and hyperfine coupling. The authors discuss in detail spin
decoherence mechanisms in metals and semiconductors. Various theories of spin
injection and spin-polarized transport are applied to hybrid structures
relevant to spin-based devices and fundamental studies of materials properties.
Experimental work is reviewed with the emphasis on projected applications, in
which external electric and magnetic fields and illumination by light will be
used to control spin and charge dynamics to create new functionalities not
feasible or ineffective with conventional electronics.Comment: invited review, 36 figures, 900+ references; minor stylistic changes
from the published versio
Coxiella burnetii Phagocytosis Is Regulated by GTPases of the Rho Family and the RhoA Effectors mDia1 and ROCK
The GTPases belonging to the Rho family control the actin cytoskeleton rearrangements needed for particle internalization during phagocytosis. ROCK and mDia1 are downstream effectors of RhoA, a GTPase involved in that process. Coxiella burnetii, the etiologic agent of Q fever, is internalized by the hostÂŽs cells in an actin-dependent manner. Nevertheless, the molecular mechanism involved in this process has been poorly characterized. This work analyzes the role of different GTPases of the Rho family and some downstream effectors in the internalization of C. burnetii by phagocytic and non-phagocytic cells. The internalization of C. burnetii into HeLa and RAW cells was significantly inhibited when the cells were treated with Clostridium difficile Toxin B which irreversibly inactivates members of the Rho family. In addition, the internalization was reduced in HeLa cells that overexpressed the dominant negative mutants of RhoA, Rac1 or Cdc42 or that were knocked down for the Rho GTPases. The pharmacological inhibition or the knocking down of ROCK diminished bacterium internalization. Moreover, C. burnetii was less efficiently internalized in HeLa cells overexpressing mDia1-N1, a dominant negative mutant of mDia1, while the overexpression of the constitutively active mutant mDia1-ÎN3 increased bacteria uptake. Interestingly, when HeLa and RAW cells were infected, RhoA, Rac1 and mDia1 were recruited to membrane cell fractions. Our results suggest that the GTPases of the Rho family play an important role in C. burnetii phagocytosis in both HeLa and RAW cells. Additionally, we present evidence that ROCK and mDia1, which are downstream effectors of RhoA, are involved in that processFil: Salinas Ojeda, Romina Paola. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Mendoza. Instituto de HistologĂa y EmbriologĂa de Mendoza Dr. Mario H. Burgos. Universidad Nacional de Cuyo. Facultad de Cienicas MĂ©dicas. Instituto de HistologĂa y EmbriologĂa de Mendoza Dr. Mario H. Burgos; ArgentinaFil: Ortiz Flores, Rodolfo Matias. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Mendoza. Instituto de HistologĂa y EmbriologĂa de Mendoza Dr. Mario H. Burgos. Universidad Nacional de Cuyo. Facultad de Cienicas MĂ©dicas. Instituto de HistologĂa y EmbriologĂa de Mendoza Dr. Mario H. Burgos; ArgentinaFil: Distel, JesĂșs SebastiĂĄn. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Mendoza. Instituto de HistologĂa y EmbriologĂa de Mendoza Dr. Mario H. Burgos. Universidad Nacional de Cuyo. Facultad de Cienicas MĂ©dicas. Instituto de HistologĂa y EmbriologĂa de Mendoza Dr. Mario H. Burgos; ArgentinaFil: Aguilera, Milton Osmar. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Mendoza. Instituto de HistologĂa y EmbriologĂa de Mendoza Dr. Mario H. Burgos. Universidad Nacional de Cuyo. Facultad de Cienicas MĂ©dicas. Instituto de HistologĂa y EmbriologĂa de Mendoza Dr. Mario H. Burgos; ArgentinaFil: Colombo, Maria Isabel. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Mendoza. Instituto de HistologĂa y EmbriologĂa de Mendoza Dr. Mario H. Burgos. Universidad Nacional de Cuyo. Facultad de Cienicas MĂ©dicas. Instituto de HistologĂa y EmbriologĂa de Mendoza Dr. Mario H. Burgos; ArgentinaFil: Beron, Walter. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Mendoza. Instituto de HistologĂa y EmbriologĂa de Mendoza Dr. Mario H. Burgos. Universidad Nacional de Cuyo. Facultad de Cienicas MĂ©dicas. Instituto de HistologĂa y EmbriologĂa de Mendoza Dr. Mario H. Burgos; Argentin
Can we improve outcome of congenital diaphragmatic hernia?
This review gives an overview of the disease spectrum of congenital diaphragmatic hernia (CDH). Etiological factors, prenatal predictors of survival, new treatment strategies and long-term morbidity are described. Early recognition of problems and improvement of treatment strategies in CDH patients may increase survival and prevent secondary morbidity. Multidisciplinary healthcare is necessary to improve healthcare for CDH patients. Absence of international therapy guidelines, lack of evidence of many therapeutic modalities and the relative low number of CDH patients calls for cooperation between centers with an expertise in the treatment of CDH patients. The international CDH Euro-Consortium is an example of such a collaborative network, which enhances exchange of knowledge, future research and development of treatment protocols
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