291 research outputs found
Ground-state properties of the one-dimensional electron liquid
We present calculations of the energy, pair-correlation function (PCF), static structure factor (SSF), and momentum density (MD) for the one-dimensional electron gas using the quantum Monte Carlo method. We are able to resolve peaks in the SSF at even-integer multiples of the Fermi wave vector, which grow as the coupling is increased. Our MD results show an increase in the effective Fermi wave vector as the interaction strength is raised in the paramagnetic harmonic wire; this appears to be a result of the vanishing difference between the wave functions of the paramagnetic and ferromagnetic systems. We have extracted the Luttinger liquid exponent from our MDs by fitting to data around kF, finding good agreement between the exponent of the ferromagnetic infinitely thin wire and the ferromagnetic harmonic wire
Coherence Length of Excitons in a Semiconductor Quantum Well
We report on the first experimental determination of the coherence length of
excitons in semiconductors using the combination of spatially resolved
photoluminescence with phonon sideband spectroscopy. The coherence length of
excitons in ZnSe quantum wells is determined to be 300 ~ 400 nm, about 25 ~ 30
times the exciton de Broglie wavelength. With increasing exciton kinetic
energy, the coherence length decreases slowly. The discrepancy between the
coherence lengths measured and calculated by only considering the acoustic
phonon scattering suggests an important influence of static disorder.Comment: 4 Pages, 4 figure
Electronic states in heterostructures formed by ultranarrow layers
Low-energy electronic states in heterosrtuctures formed by ultranarrow layer
(single or several monolayers thickness) are studied theoretically. The host
material is described within the effective mass approximation and effect of
ultranarrow layers is taken into account within the framework of the transfer
matrix approach. Using the current conservation requirement and the inversion
symmetry of ultranarrow layer, the transfer matrix is written through two
phenomenological parameters. The binding energy of localized state, the
reflection (transmission) coefficient for the single ultranarrow layer case,
and the energy spectrum of superlattice are determined by these parameters.
Spectral dependency of absorption in superlattice due to photoexcitation of
electrons from localized states into minibands is strongly dependent on the
ultranarrow layers characteristics. Such a dependency can be used for
verification of the transfer matrix parameters.Comment: 7 pages, 7 figure
A clinical case of restoration of the destroyed crown part of the tooth complicated by changes in the bifurcation area
The destruction of the tooth crown should be regarded as the cause leading over time to the disruption of the morphofunctional unity of the dentition and pathological condition of the entire dentoalveolar system. Untimely treatment of defects of hard tooth tissues leads to functional disorganization of the dentoalveolar system. The most eliminated defects are those of crowns of teeth determining the quality of aesthetics, phonetics, functions of biting and chewing. The destruction of the tooth crowns, which do not cause significant disruption of the above functions, are painless and almost asymptomatic. In such cases, deformation of the dentition and occlusion, dysfunction of masticatory muscles and temporomandibular joints as well as the development of pathological changes in periodontium occur slowly. Of great importance are the early diagnosis of pathological reconstruction of dentoalveolar system and the knowledge of pathogenesis of possible complications after the extraction of the teeth that determine the indications for prophylactic orthopedic dental treatment. The article presents a clinical case of restoration of destructed tooth crown 3.6 complicated by changes in bifurcation area. The patient underwent coronary-radicular separation with the use of cast metal cores, which allowed restoration of the sufficient size of the stump, function and anatomical shape of the tooth and hence the unity of dental arch
Superlattice formed by quantum-dot sheets: density of states and IR absorption
Low-energy continuous states of electron in heterosrtucture with periodically
placed quantum-dot sheets are studied theoretically. The Green's function of
electron is governed by the Dyson equation with the self-energy function which
is determined the boundary conditions at quantum-dot sheets with weak damping
in low-energy region. The parameters of superlattice formed by quantum-dot
sheets are determined using of the short-range model of quantum dot. The
density of states and spectral dependencies of the anisotropic absorption
coefficient under mid-IR transitions from doped quantum dots into miniband
states of superlattice strongly depend on dot concentration and on period of
sheets. These dependencies can be used for characterization of the multi-layer
structure and they determine parameters of different optoelectronic devices
exploiting vertical transport of carriers through quantum-dot sheets.Comment: 7 pages and 5 figure
- …