Gap soliton formation by nonlinear supratransmission in Bragg media

A Bragg medium in the nonlinear Kerr regime, submitted to incident cw-radiation at a frequency in a band gap, switches from total reflection to transmission when the incident energy overcomes some threshold. We demonstrate that this is a result of nonlinear supratransmission, which allows to prove that i) the threshold incident amplitude is simply expressed in terms of the deviation from the Bragg resonance, ii) the process is not the result of a shift of the gap in the nonlinear dispersion relation, iii) the transmission does occur by means of gap soliton trains, as experimentally observed [D. Taverner et al., Opt Lett 23 (1998) 328], iv) the required energy tends to zero close to the band edge.Comment: 5 figures, submitted to EuroPhysics Letter

Resonant two-wave interaction in the Davydov model

The Davydov model for exciton–phonon coupling in hydrogen-bonded molecular chains is reconsidered in the context of two-wave resonant interaction. By applying a semi-discrete slowly varying envelope approximation, when the physical problem is that of the long-distance evolution of an input finite duration excitonic pulse, we derive an integrable limit model which preserves the coupling nature of the process. The spectral transform is constructed with emphasis on the complete characterization of the spectral data. As an application, the localized one-soliton solution is explicitly constructed. Then by using Darboux–B¨ acklund transformations, a non-local (or topological) one-soliton solution is also derived. As a consequence, the system possess two different soliton solutions where the phonon component is a localized pulse, but where the exciton wave is either localized (bell shape) or topological (kink shape). The resulting approximate soliton solutions of the Davydov model in the resonant regime are subsonic in the localized case and supersonic in the topological case. Finally, by expressing the Bianchi superposition theorem, a nonlinear superposition formula is derived allowing for explicit two-soliton solution

Nonlinear energy transmission in the gap

Numerical simulations of the scattering of a linear plane wave incoming onto a nonlinear medium (sine-Gordon) reveals that: i) nonlinearity allows energy transmission in the forbidden band, ii) this nonlinear transmission occurs beyond an energy threshold of the incoming wave, iii) the process begins (at the threshold) with large amplitude breathers, and then energy is generically transmitted both by kink-antikink pairs and breathers.Comment: Latex file, 6 figures, 9 pages, to appear in Physics Letters

The Zakharov-Shabat spectral problem on the semi-line: Hilbert formulation and applications

The inverse spectral transform for the Zakharov-Shabat equation on the semi-line is reconsidered as a Hilbert problem. The boundary data induce an essential singularity at large k to one of the basic solutions. Then solving the inverse problem means solving a Hilbert problem with particular prescribed behavior. It is demonstrated that the direct and inverse problems are solved in a consistent way as soon as the spectral transform vanishes with 1/k at infinity in the whole upper half plane (where it may possess single poles) and is continuous and bounded on the real k-axis. The method is applied to stimulated Raman scattering and sine-Gordon (light cone) for which it is demonstrated that time evolution conserves the properties of the spectral transform.Comment: LaTex file, 1 figure, submitted to J. Phys.

Enhanced infection prophylaxis reduces mortality in severely immunosuppressed HIV-infected adults and older children initiating antiretroviral therapy in Kenya, Malawi, Uganda and Zimbabwe: the REALITY trial

Meeting abstract FRAB0101LB from 21st International AIDS Conference 18–22 July 2016, Durban, South Africa. Introduction: Mortality from infections is high in the first 6 months of antiretroviral therapy (ART) among HIV‐infected adults and children with advanced disease in sub‐Saharan Africa. Whether an enhanced package of infection prophylaxis at ART initiation would reduce mortality is unknown. Methods: The REALITY 2×2×2 factorial open‐label trial (ISRCTN43622374) randomized ART‐naïve HIV‐infected adults and children >5 years with CD4 <100 cells/mm3. This randomization compared initiating ART with enhanced prophylaxis (continuous cotrimoxazole plus 12 weeks isoniazid/pyridoxine (anti‐tuberculosis) and fluconazole (anti‐cryptococcal/candida), 5 days azithromycin (anti‐bacterial/protozoal) and single‐dose albendazole (anti‐helminth)), versus standard‐of‐care cotrimoxazole. Isoniazid/pyridoxine/cotrimoxazole was formulated as a scored fixed‐dose combination. Two other randomizations investigated 12‐week adjunctive raltegravir or supplementary food. The primary endpoint was 24‐week mortality. Results: 1805 eligible adults (n = 1733; 96.0%) and children/adolescents (n = 72; 4.0%) (median 36 years; 53.2% male) were randomized to enhanced (n = 906) or standard prophylaxis (n = 899) and followed for 48 weeks (3.8% loss‐to‐follow‐up). Median baseline CD4 was 36 cells/mm3 (IQR: 16–62) but 47.3% were WHO Stage 1/2. 80 (8.9%) enhanced versus 108(12.2%) standard prophylaxis died before 24 weeks (adjusted hazard ratio (aHR) = 0.73 (95% CI: 0.54–0.97) p = 0.03; Figure 1) and 98(11.0%) versus 127(14.4%) respectively died before 48 weeks (aHR = 0.75 (0.58–0.98) p = 0.04), with no evidence of interaction with the two other randomizations (p > 0.8). Enhanced prophylaxis significantly reduced incidence of tuberculosis (p = 0.02), cryptococcal disease (p = 0.01), oral/oesophageal candidiasis (p = 0.02), deaths of unknown cause (p = 0.02) and (marginally) hospitalisations (p = 0.06) but not presumed severe bacterial infections (p = 0.38). Serious and grade 4 adverse events were marginally less common with enhanced prophylaxis (p = 0.06). CD4 increases and VL suppression were similar between groups (p > 0.2). Conclusions: Enhanced infection prophylaxis at ART initiation reduces early mortality by 25% among HIV‐infected adults and children with advanced disease. The pill burden did not adversely affect VL suppression. Policy makers should consider adopting and implementing this low‐cost broad infection prevention package which could save 3.3 lives for every 100 individuals treated