757 research outputs found
Dielectric confinement of excitons in type-I and type-II semiconductor nanorods
We theoretically study the effect of the dielectric environment on the
exciton ground state of CdSe and CdTe/CdSe/CdTe nanorods. We show that
insulating environments enhance the exciton recombination rate and blueshift
the emission peak by tens of meV. These effects are particularly pronounced for
type-II nanorods. In these structures, the dielectric confinement may even
modify the spatial distribution of electron and hole charges. A critical
electric field is required to separate electrons from holes, whose value
increases with the insulating strength of the surroundings.Comment: Journal of Physics: Condensed Matter (in press
Study of moments of event shapes in e+e- annihilation using JADE data
Data from e+e- annihilation into hadrons collected by the JADE experiment at
centre-of-mass energies between 14 GeV and 44 GeV were used to study moments of
event shape distributions. The data were compared with Monte Carlo models and
with predictions from QCD NLO order calculations. The strong coupling constant
measured from the moments is alpha_S(M_Z) = 0.1286 +/- 0.0007 (stat) +/- 0.0011
(expt) +/- 0.0022 (had) +/- 0.0068 (theo), alpha_S(M_Z) = 0.1286 +/- 0.0072
(total error), consistent with the world average. However, systematic
deficiencies in the QCD NLO order predictions are visible for some of the
higher moments.Comment: JADE note 147 submitted as contributed paper to ICHEP 2004, corrected
statistical error of 6 observable average and several typo
Measurement of the Strong Coupling Constant alpha_S from the Four-Jet Rate in e+e- Annihilation using JADE data
Data from e+e- annihilation into hadrons collected by the JADE experiment at
centre-of-mass energies between 14 GeV and 44 GeV were used to study the
four-jet rate as a function of the Durham algorithm's resolution parameter
y_cut. The four-jet rate was compared to a QCD NLO order calculations including
NLLA resummation of large logarithms. The strong coupling constant measured
from the four-jet rate is alpha_S(M_Z) = 0.1169 +/- 0.0004 (stat) +/- 0.0012
(expt) +/- 0.0021 (had) +/- 0.0007 (theo), alpha_S(M_Z) = 0.1169 +/- 0.0026
(total error) in agreement with the world average.Comment: JADE note 146 submitted as contributed paper to ICHEP 200
Generalized method of image dyons for quasi-two dimensional slabs with ordinary-topological insulator interfaces
Electrostatic charges near the interface bewteen topological (TI) and
ordinary (OI) insulators induce magnetic fields in the medium that can be
described through the so-called method of image dyons (electric charge -
magnetic monopole pairs), the magnetoelectric extension of the method of image
charges in classical electrostatics. Here, we provide the expressions for the
image dyons and ensuing magnetoelectric potentials in a system comprised by two
planar-parallel OI-TI interfaces conforming a finite-width slab. The obtained
formulae extend earlier work in that they account for all different
combinations of materials forming the slab and its surroundings, including
asymmetric systems, as well as all possible combinations of external
magnetization orientations on the interfaces. The equations are susceptible of
implementation in simple computational codes, to be solved recurrently, in
order to model magnetoelectric fields in topological quantum wells, thin films,
or layers of two-dimensional materials. We exemplify this by calculating the
magnetic fields induced by a point charge in nanometer-thick quantum wells, by
means of a Mathematica code made available in repositories.Comment: 9 pages, 7 figure
Configuration interaction approach to Fermi liquid-Wigner crystal mixed phases in semiconductor nanodumbbells
Full configuration interaction calculations demonstrate the existence of mixed correlation phases in
truly three-dimensional elongated nanocrystals subject to inhomogeneous spatial confining
potentials. In such phases, the electron density behaves like a Fermi liquid in some regions, while,
simultaneously, other more dilute regions display the typical quasi-classical Wigner distribution.
The present results confirm and strengthen previous local spin-density functional theory predictions
[Ballester et al., Phys. Rev. B 82, 115405 (2010)]. Additionally, simulation of the in-plane and
z-polarized modes of the absorption spectra reveals the different correlation regimes occurring in
these system
Mixed correlation phases in elongated quantum dots
It is theoretically shown, within the local spin-density-functional theory framework, that inhomogeneous confining potentials in elongated, diluted N-electron quantum dots may lead to the formation of mixed phases in which some regions of the N-electron system behave like a Fermi liquid while, simultaneously, other, more dilute regions display quasiclassical Wigner crystallization. The characterization of the mixed phases in the addition energy spectrum and the infrared response is reported. An infrared sensor of electron filling is suggested
An intramolecular oxa-Michael reaction on α,β-unsaturated α-amino-δ-hydroxycarboxylic acid esters. Synthesis of functionalized 1,3-dioxanes
A highly diastereoselective intramolecular oxa-Michael reaction on α,β-unsaturated α-amino-δ-hydroxycarboxylic acid esters is presented; 1,3-dioxanes functionalized in positions 2,4 and 6 were obtained in good yields and with excellent selectivities; an experimental and computational study was carried out to understand the reaction course in terms of yields and selectivities. This reaction proceeds under mild reaction conditions using highly electrophilic aldehydes and ketones
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