Strain-induced energy band gap opening in two-dimensional bilayered silicon film

This work presents a theoretical study of the structural and electronic properties of bilayered silicon films under in-plane biaxial strain/stress using density functional theory. Atomic structures of the two-dimensional silicon films are optimized by using both the local-density approximation and generalized gradient approximation. In the absence of strain/stress, five buckled hexagonal honeycomb structures of the bilayered silicon film have been obtained as local energy minima and their structural stability has been verified. These structures present a Dirac-cone shaped energy band diagram with zero energy band gaps. Applying tensile biaxial strain leads to a reduction of the buckling height. Atomically flat structures with zero bucking height have been observed when the AA-stacking structures are under a critical biaxial strain. Increase of the strain between 10.7% ~ 15.4% results in a band-gap opening with a maximum energy band gap opening of ~168.0 meV obtained when 14.3% strain is applied. Energy band diagram, electron transmission efficiency, and the charge transport property are calculated.Comment: 18 pages, 5 figures, 1 tabl

Spin-phonon coupling in single Mn doped CdTe quantum dot

The spin dynamics of a single Mn atom in a laser driven CdTe quantum dot is addressed theoretically. Recent experimental results\cite{Le-Gall_PRL_2009,Goryca_PRL_2009,Le-Gall_PRB_2010}show that it is possible to induce Mn spin polarization by means of circularly polarized optical pumping. Pumping is made possible by the faster Mn spin relaxation in the presence of the exciton. Here we discuss different Mn spin relaxation mechanisms. First, Mn-phonon coupling, which is enhanced in the presence of the exciton. Second, phonon-induced hole spin relaxation combined with carrier-Mn spin flip coupling and photon emission results in Mn spin relaxation. We model the Mn spin dynamics under the influence of a pumping laser that injects excitons into the dot, taking into account exciton-Mn exchange and phonon induced spin relaxation of both Mn and holes. Our simulations account for the optically induced Mn spin pumping.Comment: 17 pages, 11 figures, submitted to PR

An automated system for global atmospheric sampling using B-747 airliners

The global air sampling program utilizes commercial aircrafts in scheduled service to measure atmospheric constituents. A fully automated system designed for the 747 aircraft is described. Airline operational constraints and data and control subsystems are treated. The overall program management, system monitoring, and data retrieval from four aircraft in global service is described

Dynamics of a nanowire superlattice in an ac electric field

With a one-band envelope function theory, we investigate the dynamics of a finite nanowire superlattice driven by an ac electric field by solving numerically the time-dependent Schroedinger equation. We find that for an ac electric field resonant with two energy levels located in two different minibands, the coherent dynamics in nanowire superlattices is much more complex as compared to the standard two-level description. Depending on the energy levels involved in the transitions, the coherent oscillations exhibit different patterns. A signature of barrier-well inversion phenomenon in nanowire superlattices is also obtained.Comment: 14 pages, 4 figure

A Study of Gaussianity in CMB band maps

The detection of non-Gaussianity in the CMB data would rule out a number of inflationary models. A null detection of non-Gaussianity, instead, would exclude alternative models for the early universe. Thus, a detection or non-detection of primordial non-Gaussianity in the CMB data is crucial to discriminate among inflationary models, and to test alternative scenarios. However, there are various non-cosmological sources of non-Gaussianity. This makes important to employ different indicators in order to detect distinct forms of non-Gaussianity in CMB data. Recently, we proposed two new indicators to measure deviation from Gaussianity on large angular scales, and used them to study the Gaussianity of the raw band WMAP maps with and without the KQ75 mask. Here we extend this work by using these indicators to perform similar analyses of deviation from Gaussianity of the foreground-reduced Q, V, and W band maps. We show that there is a significant deviation from Gaussianity in the considered full-sky maps, which is reduced to a level consistent with Gaussianity when the KQ75 mask is employed.Comment: 5 pages, 2 PS figures, uses ws-ijmpd.cls ; to be published in the International Journal of Modern Physics

We\u27ll Do Our Share : While You\u27re Over There

https://digitalcommons.library.umaine.edu/mmb-vp/5016/thumbnail.jp

I Wonder What They\u27re Doing Tonight : Your Girl And Mine

https://digitalcommons.library.umaine.edu/mmb-vp/3185/thumbnail.jp

Case History of Seismic Base Isolation of a Building –The Foothill Communities Law and Justice Center

The Foothill Communities Law and Justice Center, located in seismically active Southern California, is the first building in the United States to be base isolated for seismic resistance. Natural rubber isolators with layers of steel plates were used to make the fundamental period of vibration of the base isolated building about twice as long as that for a comparable conventional fixed base building. Most earthquake energy is present in the shorter period ranges, and at longer periods, a building should be subjected to less earthquake input; this will allow buildings to be designed more economically and increase the likelihood of less damage, both structural and non- structural. The experience of the Law and Justice Center after three small earthquakes suggest that the concept is not only feasible, but may be the wave of the future for what would be relatively short period buildings

Optoelectronics of Inverted Type-I CdS/CdSe Core/Crown Quantum Ring

Inverted type-I heterostructure core/crown quantum rings (QRs) are quantum-efficient luminophores, whose spectral characteristics are highly tunable. Here, we study the optoelectronic properties of type-I core/crown CdS/CdSe QRs in the zincblende phase - over contrasting lateral size and crown width. For this we inspect their strain profiles, transition energies, transition matrix elements, spatial charge densities, electronic bandstructure, band-mixing probabilities, optical gain spectra, maximum optical gains and differential optical gains. Our framework uses an effective-mass envelope function theory based on the 8-band k$\cdot$p method employing the valence force field model for calculating the atomic strain distributions. The gain calculations are based on the density-matrix equation and take into consideration the excitonic effects with intraband scattering. Variations in the QR lateral size and relative widths of core and crown (ergo the composition) affect their energy levels, band-mixing probabilities, optical transition matrix elements, emission wavelengths/intensity, etc. The optical gain of QRs is also strongly dimension and composition dependent with further dependency on the injection carrier density causing band-filling effect. They also affect the maximum and differential gain at varying dimensions and compositions.Comment: Published in AIP Journal of Applied Physics (11 pages, 7 figures