182,239 research outputs found
Nd-doped aluminum oxide integrated amplifiers at 880 nm, 1060 nm, and 1330 nm
Neodymium-doped Al2O3 layers were deposited on thermally oxidized Si substrates and channel waveguides were patterned using reactive-ion etching. Internal net gain on the Nd3+ transitions at 880, 1064, and 1330 nm was investigated,\ud
yielding a maximum gain of 6.3 dB/cm at 1064 nm. Values for the energy-transfer upconversion parameter for different Nd3+\ud
concentrations were deduced
Spin relaxation in diluted magnetic semiconductor quantum dots
Electron spin relaxation induced by phonon-mediated s-d exchange interaction
in a II-VI diluted magnetic semiconductor quantum dot is investigated
theoretically. The electron-acoustic phonon interaction due to piezoelectric
coupling and deformation potential is included. The resulting spin lifetime is
typically on the order of microseconds. The effectiveness of the
phonon-mediated spin-flip mechanism increases with increasing Mn concentration,
electron spin splitting, vertical confining strength and lateral diameter,
while it shows non-monotonic dependence on the magnetic field and temperature.
An interesting finding is that the spin relaxation in a small quantum dot is
suppressed for strong magnetic field and low Mn concentration at low
temperature.Comment: 11 pages, 11 figures, to be published in Phys. Rev.
Electroluminescence and photoluminescence of Ge-implanted Si/SiO_2/Si structures
Electroluminescent devices were fabricated in SiO_2 films containing Ge nanocrystals formed by ion implantation and precipitation during annealing at 900â°C, and the visible roomâtemperature electroluminescence and photoluminescence spectra were found to be broadly similar. The electroluminescent devices have an onset for emission in reverse bias of approximately â10 V, suggesting that the mechanism for carrier excitation may be an avalanche breakdown caused by injection of hot carriers into the oxide. The electroluminescent emission was stable for periods exceeding 6 h
Renormalizability of the nuclear many-body problem with the Skyrme interaction beyond mean field
Phenomenological effective interactions like Skyrme forces are currently used
in mean--field calculations in nuclear physics. Mean--field models have strong
analogies with the first order of the perturbative many--body problem and the
currently used effective interactions are adjusted at the mean--field level. In
this work, we analyze the renormalizability of the nuclear many--body problem
in the case where the effective Skyrme interaction is employed in its standard
form and the perturbative problem is solved up to second order. We focus on
symmetric nuclear matter and its equation of state, which can be calculated
analytically at this order. It is shown that only by applying specific density
dependence and constraints to the interaction parameters could
renormalizability be guaranteed in principle. This indicates that the standard
Skyrme interaction does not in general lead to a renormalizable theory. For
achieving renormalizability, other terms should be added to the interaction and
employed perturbatively only at first order.Comment: Revised versio
Single/Few Bunch Space Charge Effects at 8-GeV in the Fermilab Main Injector
For Project X, it is planned to inject a beam of 3x10**11 particles per bunch
into the Main Injector. Therefore, at 8-GeV, there will be increased space
charge tune shifts and an increased incoherent tune spread. In preparation for
these higher intensity bunches exploratory studies have commenced looking at
the transmission of different intensity bunches at different tunes. An
experiment is described with results for bunch intensities between 20 and 300
10**9 particles. To achieve the highest intensity bunches coalescing at 8-GeV
is required, resulting in a longer bunch length. Comparisons show that similar
transmission curves are obtained when the intensity and bunch length have
increased by factors of 3.2 and 3.4 respectively, indicating the incoherent
tune shifts are similar, as expected from theory. The results of these
experiments will be used in conjugation with simulations to further study high
intensity bunches in the Main Injector.Comment: 3 pp. 3rd International Particle Accelerator Conference (IPAC 2012)
20-25 May 2012, New Orleans, Louisian
A note on the sign (unit root) ambiguities of Gauss sums in index 2 and 4 cases
Recently, the explicit evaluation of Gauss sums in the index 2 and 4 cases
have been given in several papers (see [2,3,7,8]). In the course of evaluation,
the sigh (or unit root) ambiguities are unavoidably occurred. This paper
presents another method, different from [7] and [8], to determine the sigh
(unit root) ambiguities of Gauss sums in the index 2 case, as well as the ones
with odd order in the non-cyclic index 4 case. And we note that the method in
this paper are more succinct and effective than [8] and [7]
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