Dislocations in Strained-layer Semiconductor Heterostructures.

The reliability of semiconductor devices depends upon the stability of the constituent materials. Strained-layer semiconductor structures contain a layer whose lattice constant differs from the surrounding layers, resulting in a misfit strain. As dislocations are the main failure mechanism in semiconductor lasers, it is essential to establish whether the stability of these structures is affected by the lattice mismatch and the possibility of relaxation by the formation of misfit dislocations. In this thesis, dislocations in strained-layer semiconductor structures are investigated. Relaxation of strained-layer GaAs/InxGa1-xAs/GaAs heterostructures through the formation of misfit dislocations is found to occur in stages. Firstly, generation and elongation of misfit dislocations on threading dislocations during molecular beam epitaxy (MBE) growth have been demonstrated with increasing strained-layer thickness. The onset of this stage has been shown to occur at strained-layer thicknesses below those predicted by the Matthews-Blakeslee (M-B) model. The second stage of relaxation is marked by the formation of a network of 60° misfit dislocations. A third stage of relaxation has been discovered, in which pure edge (i.e. 90°) misfit dislocations are formed in addition to the existing network of 60° misfit dislocations. Different mechanisms are found to be responsible for the three stages of relaxation. The M-B model describes the transformation of threading dislocations to generate 60° misfit dislocations. As this affects individual dislocations, it results in only local relaxation. A separate mechanism, which remains unclear but is not dependent on the interactions of dislocations, dominates the formation of a 60° misfit dislocation network. The edge dislocations responsible for further relaxation of the structures are produced by vacancy-producing jogs. These protrude from pre-existing 60° dislocations and trail edge dislocation pairs as they climb. It is shown here that as-grown structures with strained-layer thicknesses below the theoretical prediction can be relaxed by the formation of a 60° dislocation network during post-growth thermal processing and bending. Thus the first two stages of relaxation are dependent on both the strained-layer thickness during fabrication, and on the temperature and applied stress of as-grown structures. Finally, dislocation motion in strained layer structures has been shown to be slower than that in unstrained structures. Thus the misfit stress acts as an additional resistant force to the displacement of atoms in non-misfit dislocations, even though it drives the formation of misfit dislocations

Study progress of CCR3 in wet age-related macular degeneration

According to the study, chemokine receptor 3(CCR3)in the eye is mainly distributed in retinal pigment epithelial cells, and also expressed in the choroidal vascular endothelial cells(CECs). The specificity of CCR3's high expression in wet age-related macular degeneration(AMD)was found, and it is proved that in wet-AMD patients, it plays an important role in the formation of choroidal neovascularization(CNV). In this paper, the structure, function, the problem of current research and the future direction of CCR3 were summarized. It is believed that with the further research on CCR3, it will not only help us to find a new method of wet-AMD diagnosis and treatment, but also may provide an important reference for other CNV disease research and new anti-CNV drugs

An evolutionary game based particle swarm optimization algorithm

AbstractParticle swarm optimization (PSO) is an evolutionary algorithm used extensively. This paper presented a new particle swarm optimizer based on evolutionary game (EGPSO). We map particles’ finding optimal solution in PSO algorithm to players’ pursuing maximum utility by choosing strategies in evolutionary games, using replicator dynamics to model the behavior of particles. And in order to overcome premature convergence a multi-start technique was introduced. Experimental results show that EGPSO can overcome premature convergence and has great performance of convergence property over traditional PSO

Noise in Genotype Selection Model

We study the steady state properties of a genotype selection model in presence of correlated Gaussian white noise. The effect of the noise on the genotype selection model is discussed. It is found that correlated noise can break the balance of gene selection and induce the phase transition which can makes us select one type gene haploid from a gene group.Comment: 8 pages, 4 figure

Possible open-charmed pentaquark molecule Ωc(3188)\Omega_c(3188) --- the DΞD \Xi bound state --- in the Bethe-Salpeter formalism

We study the $S$-wave $D\Xi$ bound state in the Bethe-Salpeter formalism in the ladder and instantaneous approximations. With the kernel generated by the hadronic effective Lagrangian, two open-charmed bound states, which quantum numbers are $I=0$, $J^P=(\frac{1}{2})^-$ and $I=1$, $J^P=(\frac{1}{2})^-$, respectively, are predicted as new candidates of hadronic pentaquark molecules in our formalism. If existing, they could contribute to the broad 3188 eV structure near the five new narrow $\Omega_c$ states observed recently by the LHCb Collaboration.Comment: 8 pages, 4 figures, accepted by Eur. Phys. J.

Current Reversals in a inhomogeneous system with asymmetric unbiased fluctuations

We present a study of transport of a Brownian particle moving in periodic symmetric potential in the presence of asymmetric unbiased fluctuations. The particle is considered to move in a medium with periodic space dependent friction. By tuning the parameters of the system, the direction of current exhibit reversals, both as a function of temperature as well as the amplitude of rocking force. We found that the mutual interplay between the opposite driving factors is the necessary term for current reversals.Comment: 9 pages, 7 figure

Starvation resistance of invasive lace bug Corythucha ciliata (Hemiptera: Tingidae) in China

Food shortage is a prevalent threat to insect survival and successful reproduction in natural settings. An insect species invading new areasmay have a high capacity to survive and adapt to starvation. To test these hypotheses, we assessed the survival time of Corythucha ciliata (Say), in a laboratory under two starvation conditions: complete starvation (no food supplied) and gradual starvation (food provided once and not replenished). Under complete starvation, survival of 3rd to 5th instar nymphs tended to decline steadily, whereas under gradual starvation this process was delayed in the initial stage. The average survival times increased as the instar increased under both conditions (14.0 h, 15.9 h and 24.4 h under complete starvation conditions; 27.8 h, 29.6 h and 33.6 h under gradual starvation conditions). The longest lived individual nymph survived for 49 hours. The results may partially explain the rapid global expansion of C. ciliata