32 research outputs found
Dynamic Coupling of Piezoelectric Effects, Spontaneous Polarization, and Strain in Lattice-Mismatched Semiconductor Quantum-Well Heterostructures
A static and dynamic analysis of the combined and self-consistent influence of spontaneous polarization, piezoelectric effects, lattice mismatch, and strain effects is presented for a three-layer one-dimensional AlN/GaN wurtzite quantum-well structure with GaN as the central quantum-well layer . It is shown that, contrary to the assumption of Fonoberov and Balandin [J. Appl. Phys. 94, 7178 (2003); J. Vac. Sci. Technol. B 22, 2190 (2004)], even in cases with no current transport through the structure, the strain distributions are not well captured by minimization of the strain energy only and not, as is in principle required, the total free energy including electric and piezoelectric coupling and spontaneous polarization contributions. Furthermore, we have found that, when an ac signal is imposed through the structure, resonance frequencies exist where strain distributions are even more strongly affected by piezoelectric-coupling contributions depending on the amount of mechanical and electrical losses in the full material system
Effects of ultrasonication on the production of hyaluronic acid by lactobacilli
The oral administration of hyaluronic acid has been shown to improve skin health. This study aimed at utilizing ultrasound treatment to enhance the production of hyaluronic acid by lactobacilli. Among the 16 strains of lactobacilli screened, a higher production of hyaluronic acid (Pâ1 to 0.385 mg mlâ1, while an amplitude of 20% yielded a lower increase ranging from 0.227 mg mlâ1 to 0.310 mg mlâ1. Increasing duration of ultrasonic treatment (from 1 min to 3 min) also significantly (P<0.05) improved the concentration of hyaluronic acid in some strains. Our data demonstrated that a sub-lethal physical treatment, such as ultrasonication, can be applied to increase the membrane permeability of lactobacilli cells and subsequently increase the release of bioactive metabolites
Second harmonic generation and birefringence of some ternary pnictide semiconductors
A first-principles study of the birefringence and the frequency dependent
second harmonic generation (SHG) coefficients of the ternary pnictide
semiconductors with formula ABC (A = Zn, Cd; B = Si, Ge; C = As, P) with
the chalcopyrite structures was carried out. We show that a simple empirical
observation that a smaller value of the gap is correlated with larger value of
SHG is qualitatively true. However, simple inverse power scaling laws between
gaps and SHG were not found. Instead, the real value of the nonlinear response
is a result of a very delicate balance between different intraband and
interband terms.Comment: 13 pages, 12 figure
Anomalous Hall effect in paramagnetic two dimensional systems
We investigate the possibility of observing the anomalous Hall effect (AHE)
in two dimensional paramagnetic systems. We apply the semiclassical equations
of motion to carriers in the conduction and valence bands of wurtzite and
zincblende quantum wells in the exchange field generated by magnetic impurities
and we calculate the anomalous Hall conductivity based on the Berry phase
corrections to the carrier velocity. We show that under certain circumstances
this conductivity approaches one half of the conductance quantum. We consider
the effect of an external magnetic field and show that for a small enough field
the theory is unaltered.Comment: 9 pages, 10 figures, 2 table
Electrostriction coefficients of GaN, AlN, MgO and ZnO in the wurtzite structure from first-principles
International audienceFirst-principles calculations have been performed on wurtzite AlN, GaN, MgO and ZnO, with a view to obtaining electrostriction coefficients. © 2009 American Institute of Physics