Investigation of phase-separated electronic states in 1.5µm GaInNAs/GaAs heterostructures by optical spectroscopy

We report on the comparative electronic state characteristics of particular GaInNAs/GaAs quantum well structures that emit near 1.3 and 1.5 µm wavelength at room temperature. While the electronic structure of the 1.3 µm sample is consistent with a standard quantum well, the 1.5 µm sample demonstrate quite different characteristics. By using photoluminescence sPLd excitation spectroscopy at various detection wavelengths, we demonstrate that the macroscopic electronic states in the 1.5 µm structures originate from phase-separated quantum dots instead of quantum wells. PL measurements with spectrally selective excitation provide further evidence for the existence of composition-separated phases. The evidence is consistent with phase segregation during the growth leading to two phases, one with high In and N content which accounts for the efficient low energy 1.5 µm emission, and the other one having lower In and N content which contributes metastable states and only emits under excitation in a particular wavelength range

Stably non-synchronizable maps of the plane

Pecora and Carroll presented a notion of synchronization where an (n-1)-dimensional nonautonomous system is constructed from a given $n$-dimensional dynamical system by imposing the evolution of one coordinate. They noticed that the resulting dynamics may be contracting even if the original dynamics are not. It is easy to construct flows or maps such that no coordinate has synchronizing properties, but this cannot be done in an open set of linear maps or flows in $\R^n$, $n\geq 2$. In this paper we give examples of real analytic homeomorphisms of $\R^2$ such that the non-synchronizability is stable in the sense that in a full $C^0$ neighborhood of the given map, no homeomorphism is synchronizable

Eigenelements of a General Aggregation-Fragmentation Model

We consider a linear integro-differential equation which arises to describe both aggregation-fragmentation processes and cell division. We prove the existence of a solution (\lb,\U,\phi) to the related eigenproblem. Such eigenelements are useful to study the long time asymptotic behaviour of solutions as well as the steady states when the equation is coupled with an ODE. Our study concerns a non-constant transport term that can vanish at $x=0,$ since it seems to be relevant to describe some biological processes like proteins aggregation. Non lower-bounded transport terms bring difficulties to find $a\ priori$ estimates. All the work of this paper is to solve this problem using weighted-norms

Indices of the iterates of ({\Bbb R}^3)-homeomorphisms at fixed points which are isolated invariant sets

Let (U \subset {\mathbb R}^3) be an open set and (f:U \to f(U) \subset {\mathbb R}^3) be a homeomorphism. Let (p \in U) be a fixed point. It is known that, if (\{p\}) is not an isolated invariant set, the sequence of the fixed point indices of the iterates of (f) at (p), ((i(f^n,p))_{n\geq 1}), is, in general, unbounded. The main goal of this paper is to show that when (\{p\}) is an isolated invariant set, the sequence ((i(f^n,p))_{n\geq 1}) is periodic. Conversely, we show that for any periodic sequence of integers ((I_n)_{n \geq1}) satisfying Dold's necessary congruences, there exists an orientation preserving homeomorphism such that (i(f^n,p)=I_n) for every (n\geq 1). Finally we also present an application to the study of the local structure of the stable/unstable sets at (p)

GaN directional couplers for integrated quantum photonics

Large cross-section GaN waveguides are proposed as a suitable architecture to achieve integrated quantum photonic circuits. Directional couplers with this geometry have been designed with aid of the beam propagation method and fabricated using inductively coupled plasma etching. Scanning electron microscopy inspection shows high quality facets for end coupling and a well defined gap between rib pairs in the coupling region. Optical characterization at 800 nm shows single-mode operation and coupling-length-dependent splitting ratios. Two photon interference of degenerate photon pairs has been observed in the directional coupler by measurement of the Hong-Ou-Mandel dip with 96% visibility.Comment: 4 pages, 5 figure

Strictly Toral Dynamics

This article deals with nonwandering (e.g. area-preserving) homeomorphisms of the torus $\mathbb{T}^2$ which are homotopic to the identity and strictly toral, in the sense that they exhibit dynamical properties that are not present in homeomorphisms of the annulus or the plane. This includes all homeomorphisms which have a rotation set with nonempty interior. We define two types of points: inessential and essential. The set of inessential points $ine(f)$ is shown to be a disjoint union of periodic topological disks ("elliptic islands"), while the set of essential points $ess(f)$ is an essential continuum, with typically rich dynamics (the "chaotic region"). This generalizes and improves a similar description by J\"ager. The key result is boundedness of these "elliptic islands", which allows, among other things, to obtain sharp (uniform) bounds of the diffusion rates. We also show that the dynamics in $ess(f)$ is as rich as in $\mathbb{T}^2$ from the rotational viewpoint, and we obtain results relating the existence of large invariant topological disks to the abundance of fixed points.Comment: Incorporates suggestions and corrections by the referees. To appear in Inv. Mat

Particle approximation of the one dimensional Keller-Segel equation, stability and rigidity of the blow-up

We investigate a particle system which is a discrete and deterministic approximation of the one-dimensional Keller-Segel equation with a logarithmic potential. The particle system is derived from the gradient flow of the homogeneous free energy written in Lagrangian coordinates. We focus on the description of the blow-up of the particle system, namely: the number of particles involved in the first aggregate, and the limiting profile of the rescaled system. We exhibit basins of stability for which the number of particles is critical, and we prove a weak rigidity result concerning the rescaled dynamics. This work is complemented with a detailed analysis of the case where only three particles interact

The multifactorial pathways towards resistance to the cytosine analogues emtricitabine and lamivudine: Evidences from literature

The article by Bulteel et al.,1 published in the September issue of the journal, has investigated the rate of M184V emergence in patients receiving HAART combinations containing efavirenz (EFV), tenofovir (TDF) and lamivudine (3 TC) or emtricitabine (FTC) within the UK Collaborative HIV Cohort. By analyzing 304 genotypic resistance tests, the authors asserted that, although patients receiving 3 TC-based regimens were more likely to develop M184V than those receiving FTC-based regimens (event rate: 0.55 [95%CI: 0.28–0.96] for 3 TC versus 0.34 [95%CI: 0.21–0.46] for FTC), this association was not statistically significant in both univariable and multivariable models. These results are different from those reported in previous studies from our and other groups2, 3 and 4 showing a significant decrease in M184V emergence in patients failing FTC + TDF-based compared to 3 TC + TDF-based HAART (Table 1). The lower prevalence of M184V in FTC-containing regimen was also supported by a recently published letter showing a strong trend (P = 0.051) towards higher rates of resistance to the 3 TC containing regimen 5.5 (1.8–12.8) per 1000 patient years when compared with the FTC containing regimens 1.7 (0.8–3.2) per 1000 patient year