On the Lichnerowicz conjecture for CR manifolds with mixed signature

We construct examples of nondegenerate CR manifolds with Levi form of signature $(p,q)$, $2\leq p\leq q$, which are compact, not locally CR flat, and admit essential CR vector fields. We also construct an example of a noncompact nondegenerate CR manifold with signature $(1,n-1)$ which is not locally CR flat and admits an essential CR vector fields. These provide counterexamples to the analogue of the Lichnerowicz conjecture for CR manifolds with mixed signature.Comment: 7 page

Microphotoluminescence study of disorder in ferromagnetic (Cd,Mn)Te quantum well

Microphotoluminescence mapping experiments were performed on a modulation doped (Cd,Mn)Te quantum well exhibiting carrier induced ferromagnetism. The zero field splitting that reveals the presence of a spontaneous magnetization in the low-temperature phase, is measured locally; its fluctuations are compared to those of the spin content and of the carrier density, also measured spectroscopically in the same run. We show that the fluctuations of the carrier density are the main mechanism responsible for the fluctuations of the spontaneous magnetization in the ferromagnetic phase, while those of the Mn spin density have no detectable effect at this scale of observation.Comment: 4 pages, 3 figure

Carrier-induced ferromagnetism in p-Zn1-xMnxTe

We present a systematic study of the ferromagnetic transition induced by the holes in nitrogen doped Zn1-xMnxTe epitaxial layers, with particular emphasis on the values of the Curie-Weiss temperature as a function of the carrier and spin concentrations. The data are obtained from thorough analyses of the results of magnetization, magnetoresistance and spin-dependent Hall effect measurements. The experimental findings compare favorably, without adjustable parameters, with the prediction of the Rudermann-Kittel-Kasuya-Yosida (RKKY) model or its continuous-medium limit, that is, the Zener model, provided that the presence of the competing antiferromagnetic spin-spin superexchange interaction is taken into account, and the complex structure of the valence band is properly incorporated into the calculation of the spin susceptibility of the hole liquid. In general terms, the findings demonstrate how the interplay between the ferromagnetic RKKY interaction, carrier localization, and intrinsic antiferromagnetic superexchange affects the ordering temperature and the saturation value of magnetization in magnetically and electrostatically disordered systems.Comment: 14 pages, 10 figure

Matter Mixing in Aspherical Core-collapse Supernovae: Three-dimensional Simulations with Single Star and Binary Merger Progenitor Models for SN 1987A

We perform three-dimensional hydrodynamic simulations of aspherical core-collapse supernovae focusing on the matter mixing in SN 1987A. The impacts of four progenitor (pre-supernova) models and parameterized aspherical explosions are investigated. The four pre-supernova models include a blue supergiant (BSG) model based on a slow merger scenario developed recently for the progenitor of SN 1987A (Urushibata et al. 2018). The others are a BSG model based on a single star evolution and two red supergiant (RSG) models. Among the investigated explosion (simulation) models, a model with the binary merger progenitor model and with an asymmetric bipolar-like explosion, which invokes a jetlike explosion, best reproduces constraints on the mass of high velocity $^{56}$Ni, as inferred from the observed [Fe II] line profiles. The advantage of the binary merger progenitor model for the matter mixing is the flat and less extended $\rho \,r^3$ profile of the C+O core and the helium layer, which may be characterized by the small helium core mass. From the best explosion model, the direction of the bipolar explosion axis (the strongest explosion direction), the neutron star (NS) kick velocity, and its direction are predicted. Other related implications and future prospects are also given

Discrete complex analysis on planar quad-graphs

We develop a linear theory of discrete complex analysis on general quad-graphs, continuing and extending previous work of Duffin, Mercat, Kenyon, Chelkak and Smirnov on discrete complex analysis on rhombic quad-graphs. Our approach based on the medial graph yields more instructive proofs of discrete analogs of several classical theorems and even new results. We provide discrete counterparts of fundamental concepts in complex analysis such as holomorphic functions, derivatives, the Laplacian, and exterior calculus. Also, we discuss discrete versions of important basic theorems such as Green's identities and Cauchy's integral formulae. For the first time, we discretize Green's first identity and Cauchy's integral formula for the derivative of a holomorphic function. In this paper, we focus on planar quad-graphs, but we would like to mention that many notions and theorems can be adapted to discrete Riemann surfaces in a straightforward way. In the case of planar parallelogram-graphs with bounded interior angles and bounded ratio of side lengths, we construct a discrete Green's function and discrete Cauchy's kernels with asymptotics comparable to the smooth case. Further restricting to the integer lattice of a two-dimensional skew coordinate system yields appropriate discrete Cauchy's integral formulae for higher order derivatives.Comment: 49 pages, 8 figure

Optical properties of multilayered porous silicon

International audienceWe present a short review of some optical devices based on multilayered porous silicon, which can be easily obtained by varying the formation current during the etching process. These include Bragg reflectors and Fabry–Pérot microcavities, which can be adjusted from the visible to the near infrared. The interface roughness, tragic in the case of multilayers, is studied. It can be drastically reduced when changing the electrolyte viscosity. The high reflectivities obtained in this way are measured by Cavity Ring–Down Spectroscopy. Problems occurring when realising thin layers and an efficient way to adjust precisely the optical thicknesses of the thin layers constituting the multilayered structure are also presented. Finally we present a method of calculation of the emission which takes absorption into account and is able to explain the angular dependence of the luminescence

WAT-A-GAME: sharing water and policies in your own basin

40th Annual Conference, Int. Simulation And Gaming Association, Singapour, SGP, 29-/06/2009 - 03/07/2009International audienceAfter having designed and used various games for learning and supporting water management and governance, many similarities appear. However, the components, topologies, and social and political setting of the basins are different. Therefore we have started designing andvalidating a new generic game platform, WAT-A-GAME, alias AMANZI. This new game aims at facilitating exploration and transformation of water management and water use at the small catchment scale. It gives a simple but enlightening view of the various consequences of individual and collective choices, including regulation policies. After comparing it with some previous games, we discuss its main rationales and features. We show how it can be adapted to very different settings, how players can usefully contribute to designing an instance, and how it can especially address dialogue between multi-level stakeholders. We describe an application in South-Africa, in the Inkomati basin and the preliminary results of this instance

Excitonic giant Zeeman effect in GaN:Mn^3+

We describe a direct observation of the excitonic giant Zeeman splitting in (Ga,Mn)N, a wide-gap III-V diluted magnetic semiconductor. Reflectivity and absorption spectra measured at low temperatures display the A and B excitons, with a shift under magnetic field due to s,p-d exchange interactions. Using an excitonic model, we determine the difference of exchange integrals between Mn^3+ and free carriers in GaN, N_0(alpha-beta)=-1.2 +/- 0.2 eV. Assuming a reasonable value of alpha, this implies a positive sign of beta which corresponds to a rarely observed ferromagnetic interaction between the magnetic ions and the holes.Comment: 4 pages, 4 figure

Ferromagnetic (Ga,Mn)N epilayers versus antiferromagnetic GaMn3_3N clusters

Mn-doped wurtzite GaN epilayers have been grown by nitrogen plasma-assisted molecular beam epitaxy. Correlated SIMS, structural and magnetic measurements show that the incorporation of Mn strongly depends on the conditions of the growth. Hysteresis loops which persist at high temperature do not appear to be correlated to the presence of Mn. Samples with up to 2% Mn are purely substitutional Ga$_{1-x}$Mn$_x$N epilayers, and exhibit paramagnetic properties. At higher Mn contents, precipitates are formed which are identified as GaMn$_3$N clusters by x-ray diffraction and absorption: this induces a decrease of the paramagnetic magnetisation. Samples co-doped with enough Mg exhibit a new feature: a ferromagnetic component is observed up to $T_c\sim175$ K, which cannot be related to superparamagnetism of unresolved magnetic precipitates.Comment: Revised versio

Acquired epidermodysplasia verruciformis due to multiple and unusual HPV infection among vertically-infected, HIV-positive adolescents in Zimbabwe.

BACKGROUND: We have previously described the presentation of epidermodysplasia verruciformis (EV)-like eruptions in almost a quarter of hospitalized adolescents with vertically-acquired human immunodeficiency virus (HIV) infection in Harare, Zimbabwe, a region with a high prevalence of HIV infection. METHODS: We performed a clinical case note review and skin biopsy from affected sites in 4 HIV-infected adolescents with EV-like lesions in Harare. Biopsies were processed for histology and for human papillomavirus (HPV) typing. RESULTS: All patients had long-standing skin lesions that pre-dated the diagnosis of HIV by several years. The histology of skin biopsies from all patients was consistent with EV. In each biopsy, EV-associated β-HPV type 5 was identified (additionally, type 19 was found in 1 biopsy). Cutaneous wart-associated HPV types 1 and 2 were detected in all biopsies, together with genital lesion-associated HPV types 6, 16, and 52, (as well as ≥3 other genital lesion-associated HPV types). Despite immune reconstitution with combination antiretroviral therapy (cART), there was no improvement in EV-like lesions in any patient. CONCLUSIONS: EV is a disfiguring and potentially stigmatizing condition among this patient group and is difficult to treat; cART appears to have no impact on the progression of skin disease. Among adolescents with longstanding HIV-induced immunosuppression and with high levels of sun exposure, close dermatological surveillance for potential skin malignancy is required