The multicomponent 2D Toda hierarchy: Discrete flows and string equations

The multicomponent 2D Toda hierarchy is analyzed through a factorization problem associated to an infinite-dimensional group. A new set of discrete flows is considered and the corresponding Lax and Zakharov--Shabat equations are characterized. Reductions of block Toeplitz and Hankel bi-infinite matrix types are proposed and studied. Orlov--Schulman operators, string equations and additional symmetries (discrete and continuous) are considered. The continuous-discrete Lax equations are shown to be equivalent to a factorization problem as well as to a set of string equations. A congruence method to derive site independent equations is presented and used to derive equations in the discrete multicomponent KP sector (and also for its modification) of the theory as well as dispersive Whitham equations.Comment: 27 pages. In the revised paper we improved the presentatio

Strain balanced quantum posts

Quantum posts are assembled by epitaxial growth of closely spaced quantum dot layers, modulating the composition of a semiconductor alloy, typically InGaAs. In contrast with most self-assembled nanostructures, the height of quantum posts can be controlled with nanometer precision, up to a maximum value limited by the accumulated stress due to the lattice mismatch. Here we present a strain compensation technique based on the controlled incorporation of phosphorous, which substantially increases the maximum attainable quantum post height. The luminescence from the resulting nanostructures presents giant linear polarization anisotropy.Comment: Submitted to Applied Physics Letters (7th March 2011). 4 pages, 4 figure

Etiology, epidemiology and clinical characteristics of acute moderate-to-severe diarrhea in children under 5 years of age hospitalized in a referral pediatric hospital in Rabat, Morocco

The objective of the study was to describe the etiology, epidemiology, and clinical characteristics of the principal causes of acute infectious diarrhea requiring hospitalization among children under 5 years of age in Rabat, Morocco. A prospective study was conducted from March 2011 to March 2012, designed to describe the main pathogens causing diarrhea in hospitalized children >2 months and less than 5 years of age. Among the 122 children included in the study, Enteroaggregative E. coli (EAEC) and rotavirus were the main etiologic causes of diarrhea detected. Twelve (9.8%) children were referred to the intensive care unit, while 2, presenting infection by EAEC and EAEC plus a Shigella sonnei respectively, developed a hemolytic uremic syndrome. Additionally, 6 (4.9%) deaths occurred with EAEC being isolated in four of these cases. Diarrheogenic E. coli and rotavirus play a significant role as the two main causes of severe diarrhea while other pathogens such as norovirus or parasites seem to have a minimal contribution. Surveillance and prevention programs to facilitate early recognition and improved management of potentially life-threatening diarrhea-episodes are needed

THE AVIFAUNA OF THE RÍO TIGRE BASIN, NORTHERN PERÚ

ABSTRACT ∙ The Tigre river basin in the Amazonian lowlands of northern Perú harbors a hyperdiverse avifauna that remains under‐surveyed and poorly known. We conducted the first comprehensive ornithological inventory of the basin. Observational fieldwork at 42 sites spread across the Peruvian portion of the basin resulted in a bird list of 584 species, reflecting several noteworthy patterns in the avian biogeography of northern Perú. These patterns include the distribution of several species that specialize on nutrient‐poor habitats, such as weathered clay terraces and peatlands. Peatland forests are especially poorly studied in Perú and represent a novel habitat association for these species. We also report on the presence of a suite of species with primarily montane distributions that occur in low density across the Amazonian lowlands and in the study area. Current conservation challenges in the Tigre basin include deforestation and pollution associated with hydrocarbons extraction and infrastructure projects.RESUMEN ∙ Avifauna de la cuenca del río Tigre, Perú La cuenca del río Tigre en las tierras bajas del norte de la Amazonía peruana tiene una avifauna súper diversa que sin embargo es muy poco conocida. Realizamos el primer inventario ornitológico de la cuenca. Observaciones de aves en 42 sitios resultaron en una lista de 584 especies de aves registradas en la zona de estudio. Un grupo particular de esta comunidad de aves son aquellas que se distribuyen en los bosques arcillosos pobres a lo largo del río Pucacuro y sobre bosques de turberas en el bajo río Tigre. Reportamos especies generalmente consideradas como especies facultativas u obligadas de hábitats de suelos de arena blanca en la zona de estudio. Los bosques sobre turberas aún se encuentran muy poco estudiados por los ornitólogos y representan un nuevo espacio para las especies que por lo general encontramos sobre los bosques de arena blanca. Adicionalmente reportamos un grupo de especies que generalmente son comunes en el pie de monte andino, pero que ocurren en bajas densidades en el área de estudio. Las amenazas actuales a la conservación de la zona incluyen la deforestación y la contaminación asociada con actividades petroleras y proyectos de infraestructura

Combination of searches for Higgs boson pairs in pp collisions at s=13TeV with the ATLAS detector

This letter presents a combination of searches for Higgs boson pair production using up to 36.1 fb−1 of proton–proton collision data at a centre-of-mass energy s=13 TeV recorded with the ATLAS detector at the LHC. The combination is performed using six analyses searching for Higgs boson pairs decaying into the bb¯bb¯, bb¯W+W−, bb¯τ+τ−, W+W−W+W−, bb¯γγ and W+W−γγ final states. Results are presented for non-resonant and resonant Higgs boson pair production modes. No statistically significant excess in data above the Standard Model predictions is found. The combined observed (expected) limit at 95% confidence level on the non-resonant Higgs boson pair production cross-section is 6.9 (10) times the predicted Standard Model cross-section. Limits are also set on the ratio (κλ) of the Higgs boson self-coupling to its Standard Model value. This ratio is constrained at 95% confidence level in observation (expectation) to −5.0<κλ<12.0 (−5.8<κλ<12.0). In addition, limits are set on the production of narrow scalar resonances and spin-2 Kaluza–Klein Randall–Sundrum gravitons. Exclusion regions are also provided in the parameter space of the habemus Minimal Supersymmetric Standard Model and the Electroweak Singlet Model

Search for flavour-changing neutral currents in processes with one top quark and a photon using 81 fb−1 of pp collisions at s=13TeV with the ATLAS experiment

A search for flavour-changing neutral current (FCNC) events via the coupling of a top quark, a photon, and an up or charm quark is presented using 81 fb−1 of proton–proton collision data taken at a centre-of-mass energy of 13 TeV with the ATLAS detector at the LHC. Events with a photon, an electron or muon, a b-tagged jet, and missing transverse momentum are selected. A neural network based on kinematic variables differentiates between events from signal and background processes. The data are consistent with the background-only hypothesis, and limits are set on the strength of the tqγ coupling in an effective field theory. These are also interpreted as 95% CL upper limits on the cross section for FCNC tγ production via a left-handed (right-handed) tuγ coupling of 36 fb (78 fb) and on the branching ratio for t→γu of 2.8×10−5 (6.1×10−5). In addition, they are interpreted as 95% CL upper limits on the cross section for FCNC tγ production via a left-handed (right-handed) tcγ coupling of 40 fb (33 fb) and on the branching ratio for t→γc of 22×10−5 (18×10−5)