1,036 research outputs found
Surface acoustic wave modulation of single photon emission from GaN/InGaN nanowire quantum dots
On-chip quantum information processing requires controllable quantum light
sources that can be operated on-demand at high-speeds and with the possibility
of in-situ control of the photon emission wavelength and its optical
polarization properties. Here, we report on the dynamic control of the optical
emission from core-shell GaN/InGaN nanowire (NW) heterostructures using radio
frequency surface acoustic waves (SAWs). The SAWs are excited on the surface of
a piezoelectric lithium niobate crystal equipped with a SAW delay line onto
which the NWs were mechanically transferred. Luminescent quantum dot (QD)-like
exciton localization centers induced by compositional fluctuations within the
InGaN nanoshell were identified using stroboscopic micro-photoluminescence
(micro-PL) spectroscopy. They exhibit narrow and almost fully linearly
polarized emission lines in the micro-PL spectra and a pronounced anti-bunching
signature of single photon emission in the photon correlation experiments. When
the nanowire is perturbed by the propagating SAW, the embedded QD is
periodically strained and its excitonic transitions are modulated by the
acousto-mechanical coupling, giving rise to a spectral fine-tuning within a
~1.5 meV bandwidth at the acoustic frequency of ~330 MHz. This outcome can be
further combined with spectral detection filtering for temporal control of the
emitted photons. The effect of the SAW piezoelectric field on the QD charge
population and on the optical polarization degree is also observed. The
advantage of the acousto-optoelectric over other control schemes is that it
allows in-situ manipulation of the optical emission properties over a wide
frequency range (up to GHz frequencies).Comment: arXiv admin note: text overlap with arXiv:1902.0791
Automated quantitative analysis of single and double label autoradiographs
A method for the analysis of silver grain content in both single and double label autoradiographs is presented. The total grain area is calculated by counting the number of pixels at which the recorded light intensity in transmission dark field illumination exceeds a selected threshold. The calibration tests included autoradiographs with low (3H- thymidin) and high (3H-desoxyuridin) silver grain density. The results are proportional to the customary visual grain count. For the range of visibly countable grain densities in single labeled specimens, the correlation coefficient between the computed values and the visual grain counts is better than 0.96. In the first emulsion of the two emulsion layer autoradiographs of double labeled specimens (3H-14C- thymidin) the correlation coefficient is 0.919 and 0.906. The method provides a statistical correction for the background grains not due to the isotope. The possibility to record 14C tracks by shifting the focus through the second emulsion of the double labeled specimens is also demonstrated. The reported technique is essentially independent of size, shape and density of the grains
Restriction of measles virus gene expression in acute and subacute encephalitis in Lewis rats
No abstract availabl
Ring-shaped spatial pattern of exciton luminescence formed due to the hot carrier transport in a locally photoexcited electron-hole bilayer
A consistent explanation of the formation of a ring-shaped pattern of exciton
luminescence in GaAs/AlGaAs double quantum wells is suggested. The pattern
consists of two concentric rings around the laser excitation spot. It is shown
that the luminescence rings appear due to the in-layer transport of hot charge
carriers at high photoexcitation intensity. Interestingly, one of two causes of
this transport might involve self-organized criticality (SOC) that would be the
first case of the SOC observation in semiconductor physics. We test this cause
in a many-body numerical model by performing extensive molecular dynamics
simulations. The results show good agreement with experiments. Moreover, the
simulations have enabled us to identify the particular kinetic processes
underlying the formation of each of these two luminescence rings.Comment: 14 pages, 16 figures. Final versio
Light emission and spin-polarised hole injection in InAs/GaAs quantum dot heterostructures with Schottky contact
EPL draftWe demonstrate the feasibility to obtain electroluminescence (EL), up to room temperature, from InGaAs self-assembled quantum dots (QDs) included in a forward-biased Schottky
diode. Moreover, using a ferromagnet (FM) as the contact layer, sizable circular polarization of
the EL emission in the presence of an external magnetic eld is obtained. A resonant behav-
ior of the degree of circular polarization (P) as a function of applied voltage (V ), for a given
value of magnetic eld, is observed. We explain our ndings using a model including tunneling
of (spin-polarised) holes through the metal-semiconductor interface, transport in the near surface
region of the heterostructure and out-of-equilibrium statistics of the injected carriers occupying
the available states in the QD heterostructure. In particular, the resonant P(V ) dependence is
related to the splitting of the qusi-Fermi level for two spin orientations in the FM.FCT, Portugal (project
POCI/FIS/58524/2004), the RFBR, Russia (grant 10-02-
00501), MEC (grants MAT2008-01555, QOIT-CSD2006-
00019) and CAM (S-2009/ESP-1503) (Spain)
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8 GeV beam line optics optimization for the rapid antiproton transfers at Fermilab
Tevatron Run-II upgrade requires a significant increase of the efficiency and speed of the antiproton transfers from the Accumulator to the Recycler. The goal for the total transfer time is challenging a reduction from 1 hour down to a few minutes. Here we discuss the beam line optics aspects of this project. Results of lattice measurements and optimization are analyzed in terms of transport efficiency and stability
A Simple Operator Check of the Effective Fermion Mode Function during Inflation
We present a relatively simple operator formalism which reproduces the
leading infrared logarithm of the one loop quantum gravitational correction to
the fermion mode function on a locally de Sitter background. This rule may
serve as the basis for an eventual stochastic formulation of quantum gravity
during inflation. Such a formalism would not only effect a vast simplification
in obtaining the leading powers of at fixed loop orders, it would also
permit us to sum the series of leading logarithms. A potentially important
point is that our rule does not seem to be consistent with any simple infrared
truncation of the fields. Our analysis also highlights the importance of spin
as a gravitational interaction that persists even when kinetic energy has
redshifted to zero.Comment: 39 pages, no figuire.(1) New version has clarified the ultimate
motivation by adding sentences to the abstract and to the penultimate
paragraph of the introduction. (2) By combining a number of references and
equations we have managed to reduce the length by 2 page
Optimization of 68Ga production at an 18 MeV medical cyclotron with solid targets by means of cross-section measurement of 66Ga, 67Ga and 68Ga.
The future development of personalized nuclear medicine relies on the availability of novel medical radionuclides. In particular, radiometals are attracting considerable interest since they can be used to label both proteins and peptides. Among them, the β+-emitter 68Ga is widely used in nuclear medicine for positron emission tomography (PET). It is used in theranostics as the diagnostic partner of the therapeutic β--emitters 177Lu and 90Y for the treatment of a wide range of diseases, including prostate cancer. Currently, 68Ga is usually obtained via 68Ge/68Ga generators. However, their availability, high price and limited produced radioactivity per elution are a major barrier for a wider use of the 68Ga-based diagnostic radiotracers. A promising solution is the production of 68Ga by means of proton irradiation of enriched 68Zn liquid or solid targets. Along this line, a research program is ongoing at the Bern medical cyclotron, equipped with a solid target station. In this paper, we report on the measurements of 68Ga, 67Ga and 66Ga production cross-sections using natural Zn and enriched 68Zn material, which served as the basis to perform optimized 68Ga production tests with enriched 68Zn solid targets
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