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Electronic structure, optical properties, and lattice dynamics in atomically thin indium selenide flakes

Nano Research 2014年第10期7卷 1556-1568页

作者： Juan F. Sanchez-Royo Suillermo Munoz-Matutano Mauro Brotons-Gisbert Juan P. Martinez-Pastor Alfredo Segura Andres Cantarero Rafael Mata josep Canet-Ferrer Gerard Tobias Enric Canadell jose marques-hueso Brian D. Gerardot ICMUV Instituto de Oencia de Materiales Universidad de Valencia P.O. Box 22085 46071 Valencia Spain MALTA-Consolider Team Institut de Ciencia dels Materials-Dpto. de Fisica Apficada Universitat de Valencia E-46100 Burjassot (Valencia) Spain Institut de Ciencia de Materials de Barcelona (ICMAB-CSIC) Campus de la UAB 08193 Bellaterra Barcelona Spain Institute of Photonics and Quantum Science SUPA Hefiot-Watt University Edinburgh EH14 4AS UK

The progressive stacking of chalcogenide single layers gives rise to two- dimensional semiconducting materials with tunable properties that can be exploited for new field-effect transistors and photonic devices. Yet the properties of some members of the chalcogenide family remain unexplored. Indium selenide （InSe） is attractive for applications due to its direct bandgap in the near infrared, controllable p- and n-type doping and high chemical stability. Here, we reveal the lattice dynamics, optical and electronic properties of atomically thin InSe flakes prepared by micromechanical cleavage. Raman active modes stiffen or soften in the flakes depending on which electronic bonds are excited. A progressive blue-shift of the photoluminescence peaks is observed for decreasing flake thickness （as large as 0.2 eV for three single layers）. First-principles calculations predict an even larger increase in the bandgap, 0.40 eV, for three single layers, and as much as 1.1 eV for a single layer. These results are promising from the point of view of the versatility of this material for optoelectronic applications at the nanometer scale and compatible with Si and III-V technologies.

关键词： indium selenide two-dimensional flakes micro-Raman spectroscopy micro-photoluminescence electronic structure

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Memory for location and visual cues in white-eared hummingbirds Hylocharis leucotis

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Current Zoology 2011年第4期57卷 468-476页

作者： Guillermo PEREZ Carlos LARA jose VICCON-PALE Martha SIGNORET-POILLON Doctorado en Ciencias Biologicas Universidad Autonoma Metropolitana. Unidad Xochimilco. Calzada del Hueso 1100 Col. Villa Quietud 04960 Moxico D.F. Moxico Laboratorio de Ecologfa de la Conducta Centro Tlaxcala de Biologfa de la Conducta UAT-UNAM Km 1.5 carretera Tlaxcala- Puebla s/n Colonia Xicohtoncatl Apdo. Postal 262 Tlaxcala Tlaxcala 90070 Moxico. Departamento el Hombre y su Ambiente. Universidad Autdnoma Metropolitana. Unidad Xochimilco. Calzada del hueso 1100 Col. Villa Quietud 04960 MExico D.F. Mexico

In nature hummingbirds face floral resources whose availability, quality and quantity can vary spatially and temporally. Thus, they must constantly make foraging decisions about which patches, plants and flowers to visit, partly as a function of the nectar reward. The uncertainty of these decisions would possibly be reduced if an individual could remember locations or use visual cues to avoid revisiting recently depleted flowers. In the present study, we carried out field experiments with white-eared hummingbirds Hylocharis leucotis, to evaluate their use of locations or visual cues when foraging on natural flowers Penstemon roseus. We evaluated the use of spatial memory by observing birds while they were foraging between two plants and within a single plant. Our results showed that hummingbirds prefer to use location when foraging in two plants, but they also use visual cues to efficiently locate unvisited rewarded flowers when they feed on a single plant. However, in absence of visual cues, in both experiments birds mainly used the location of previously visited flowers to make subsequent visits. Our data suggest that hummingbirds are capable of learning and employing this flexibility depending on the faced environmental conditions and the information acquired in previous visits [Current Zoology 57 （4）： 468-476, 2011].

关键词： Visual cues Location White-eared hummingbird Foraging

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Virulence Markers in Staphylococcus aureus Strains Isolated from Hemodialysis Catheters of Mexican Patients

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Advances in Microbiology 2012年第4期2卷 476-487页

作者： Gloria Paniagua-Contreras Teresita Sainz-Espunes Eric Monroy-Perez jose Raymundo Rodriguez-Moctezuma Diego Arenas-Aranda Erasmo Negrete-Abascal Sergio Vaca FES-Iztacala Universidad Nacional Autonoma de Mexico(UNAM)TlalnepantlaMéxico Ciencias Biológicas y de la Salud Universidad Autonoma Metropolitana(UAM)—XochimilcoCalzada del HuesoMéxico Departamento de Sistemas Biológicos División de Ciencias Biológicas y de la SaludUniversidad Autonoma Metropolitana(UAM)—XochimilcoCalzada del HuesoMéxico Hospital General Regional 72 Instituto Mexicano del Seguro SocialGustavo Baz Esquina F.GómezTlalnepantlaMéxico

Methicillin-resistant Staphylococcus aureus is an increasingly important cause of nosocomial bacterial infections worldwide. S. aureus is responsible for several pathologies, including skin infections, endocarditis, meningitis, deep-tissue ulcers, and sepsis. S. aureus biofilm formation on catheters and other medical devices is a major post-operative concern, because biofilms are often the source of persistent and difficult to treat bacterial infections. While catheter-related S. aureus infections have been reported, the strains responsible for these infections have not been genetically characterized. We genetically characterized S. aureus strains isolated from hemodialysis catheters in Mexican patients. The frequency of 35 genes coding for adhesins, toxins, and other virulence-associated products in the 55 isolated S. aureus strains was determined using PCR, while real-time PCR was used to examine the level of gene expression. Of the 55 S. aureus strains isolated from 109 patients, 45 (81.8%) were determined to be methicillin-resistant. The icaA, rbf, sarA, and agr genes are involved in biofilm formation and bacterial dispersion and were detected in 96.3%, 40.0%, 74.5%, and 100% of S. aureus strains, respectively, and 70.9% of the strains formed a detectable biofilm. Interestingly, 67.2% of the strains contained the icaA, agr, spa, clfA, sdrC, sdrD, sdrE, seg, seh, and sei genes, suggesting that this gene combination is important for successful catheter colonization. The results of this study provide significant insight into the virulence gene make-up of catheter-colonizing S. aureus strains, and will assist in developing a more targeted treatment approach for persistent S. aureus biofilm contamination of medical devices.

关键词： S.aureus Hemodialysis Catheter Genotyping

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