Photoexcitation of graphene with twisted light

We study theoretically the interaction of twisted light with graphene. The light-matter interaction matrix elements between the tight-binding states of electrons in graphene are determined near the Dirac points. We examine the dynamics of the photoexcitation process by posing the equations of motion of the density matrix and working up to second order in the field. The time evolution of the angular momentum of the photoexcited electrons and their associated photocurrents are examined in order to elucidate the mechanisms of angular momentum transfer. We find that the transfer of spin and orbital angular momentum from light to the electrons is more akin here to the case of intraband than of interband transitions in semiconductors, due to the fact that the two relevant energy bands of graphene originate from the same atomic orbitals.Comment: 18 pages, 4 figure

Química de los aceites esenciales del arbusto Lippia alba (Verbenaceae) de México y Costa Rica

ABSTRACT: Introduction: Lippia is a Verbenaceous genus of flowering plants, which has about 200 species, distributed throughout the southern USA, Mexico, and Central America to South America. Objective: To study and compare the chemical compositions of the essential oils of L. alba growing in Mexico and Costa Rica. Methods: The essential oils were obtained by hydrodistillation in a Clevenger-type apparatus. The chemical composition of the oils was analyzed by capillary GC-FID and GC-MS using the retention indices on a DB-5 type capillary column in addition to mass spectral fragmentation patterns. Results: A total of 65 compounds were identified in the essential oil samples from both countries, accounting for 96,5-98,1% of the total amount of the oils. The main constituents of the Mexican sample were 1,8-cineole (22,3%), myrcenone (11,2%), myrcene (10,9%), (E)-ocimenone (10,7%), (Z)-ocimenone (7,5%), and sabinene (6,8%), while for essential oil from Costa Rica the major compounds were myrcenone (30,4%), 1,8-cineole (21,4%), myrcene (11,0%), hedycaryol (4,4%), and sabinene (4,3%). Samples from both countries can be classified as belonging to chemotype “tagetenone”. Lippia alba (strong form) from Costa Rica produces essential oil that differs from all other essential oils of L. alba studied to date because it contained the sesquiterpenoids hedycaryol and the isomeric alcohols α-eudesmol, β-eudesmol, and γ-eudesmol. Conclusion: L. alba (strong form) from Costa Rica can be classified as a new subtype of the chemotype “tagetenone” (chemotype II).RESUMEN. “Química de los aceites esenciales del arbusto Lippia alba (Verbenaceae) de México y Costa Rica.” Introducción: Lippia (Verbenaceae) consta de ca. 200 especies, distribuidas a través del sur de Estados Unidos, México, América Central, el Caribe y hasta el Cono Sur de América del Sur. Objetivo: Estudiar y comparar la composición química de los aceites esenciales de L. alba de México y Costa Rica. Métodos: La extracción de los aceites se efectuó mediante hidrodestilación con un equipo Clevenger modificado. La composición química del aceite se analizó mediante las técnicas GC-FID y GC-MS. Para la identificación de los constituyentes se calcularon los índices de retención obtenidos en una columna capilar tipo DB-5, y se estudiaron los espectros de masas de cada constituyente. Resultados: Se identificaron en total 65 compuestos en las muestras de ambos países, correspondientes a un 96,5-98,1% de los constituyentes totales de los aceites. Los componentes mayoritarios de la muestra de aceite mexicana fueron 1,8-cineol (22,3%), mircenona (11,2%), mirceno (10,9%), (E)-ocimenona (10,7%), (Z)-ocimenona (7,5%) y sabineno (6,8%); y los compuestos mayoritarios de la muestra de L. alba de Costa Rica fueron mircenona (30,4%), 1,8-cineol (21,4%), mirceno (11,0%), hedicariol (4,4%) y sabineno (4,3%). Ambas muestras estudiadas en este trabajo se clasifican como pertenecientes al quimiotipo “tagetenona”. Lippia alba (forma fuerte) de Costa Rica produce un aceite que se diferencia de todos los otros aceites de L. alba estudiados a la fecha porque contienen el sesquiterpenoide hedicariol y los alcoholes isoméricos α-eudesmol, β-eudesmol y γ-eudesmol. Conclusión: L. alba (forma fuerte) se puede considerar como un nuevo subtipo perteneciente al quimiotipo “tagetenona” (quimiotipo II)

Análisis del enfoque de historia y filosofía de la ciencia en libros de texto de química : el caso de la estructura atómica

Este trabajo analiza desde el enfoque de historia y filosofía de las ciencias (HFC) la forma como se presenta el tema de estructura atómica en cinco libros de texto (LT) de los cursos de química de primer año de la Universidad de Barcelona. En el análisis se aplicó un marco metodológico que exploró la posibilidad de emplear diferentes metodologías (heterogéneas entre sí) para lograr una explicación más acertada del tema de estudio. Los resultados mostraron que la mayoría de los textos presentan una imagen de la ciencia desconectada de otros contextos, incluido el científico, imagen caracterizada por descubrimientos aislados producto del trabajo de científicos individuales. Esta representación de la ciencia no revela lo que realmente es y la manera como se genera el conocimiento científico. Además, los libros de texto analizados enfatizan el trabajo experimental, pero no cubren los detalles teóricos y si lo hacen es someramente.History and Philosophy of Science approach (HPS) in atomic structure chapters was analyzed in five chemistry textbooks that are recommended in first year's courses the at University of Barcelona. A methodological framework composed by four heterogeneous methodologies was applied in this work trying to get a more accurate explanation about the topic studied. Results have shown that a wrong image of science, disconnected from other contexts, included the scientific one, is presented in the most of the textbooks. Science in these textbooks is characterized by isolated discoveries, product of individual scientific work. This kind of scientific work's representation is not faithful with the way in which science really works and how science really is. Besides, the textbooks analyzed emphasize experimental details while they do not go into theoretical aspects in depth

Emergence of the pointer basis through the dynamics of correlations

We use the classical correlation between a quantum system being measured and its measurement apparatus to analyze the amount of information being retrieved in a quantum measurement process. Accounting for decoherence of the apparatus, we show that these correlations may have a sudden transition from a decay regime to a constant level. This transition characterizes a non-asymptotic emergence of the pointer basis, while the system-apparatus can still be quantum correlated. We provide a formalization of the concept of emergence of a pointer basis in an apparatus subject to decoherence. This contrast of the pointer basis emergence to the quantum to classical transition is demonstrated in an experiment with polarization entangled photon pairs.Comment: 4+2 pgs, 3 figures. Title changed. Revised version to appear on PR

Diacritical study of light, electrons, and sound scattering by particles and holes

We discuss the differences and similarities in the interaction of scalar and vector wave-fields with particles and holes. Analytical results are provided for the transmission of isolated and arrayed small holes as well as surface modes in hole arrays for light, electrons, and sound. In contrast to the optical case, small-hole arrays in perforated perfect screens cannot produce acoustic or electronic surface-bound states. However, unlike electrons and light, sound is transmitted through individual holes approximately in proportion to their area, regardless their size. We discuss these issues with a systematic analysis that allows exploring both common properties and unique behavior in wave phenomena for different material realizations.Comment: 3 figure

Gas Exchange Relations of Ungrafted Grapevines (cv. Carménère) Growing Under Irrigated Field Conditions

A study was carried out to evaluate the leaf gas exchange relations and water-use efficiency (WUE) of ungrafted Carménère (Vitis vinifera L.) grapevines growing under field conditions and different levels of water stress. Stomatal conductance (gs), transpiration (E), net CO2 assimilation (AN) and stem water potential (Ψs) were measured at midday in a drip-irrigated commercial vineyard located in the Maule Valley (Chile) during three growing seasons (2005 to 2009). In addition, the instantaneous (AN/E) and intrinsic (AN/gs) water-use efficiencies and stomatal sensitivity factor (k) were estimated for the own-rooted grapevines. In this study a significant non-linear relationship was observed between AN and gs (r2 = 0.82), with values of AN decreasing from 14.9 to 3.5 μmol/m2/sec as gs diminished from 0.5 to 0.05 mol/m2/sec. This resulted in a progressive increase in WUEi (intrinsic water use efficiency). A significant linear relationship was observed between Ψs and gs (r2 = 0.39) for measurements taken before and after véraison, with an increasing scattering from -1.6 to -0.4 MPa. Finally, k decreased as water stress increased, with values of 234 and 120 for no and severe water stress respectively, while k ranged from 264 to 480 and 255 to 297 for the measurements taken before and after véraison respectively. Based on the results obtained in the present study, the cultivar Carménère could be classified as drought tolerant at low water potentials, with a large range of physiological parameters changing in response to water stress

Arsenic metabolism in high altitude modern stromatolites revealed by metagenomic analysis

Modern stromatolites thrive only in selected locations in the world. Socompa Lake, located in the Andean plateau at 3570 masl, is one of the numerous extreme Andean microbial ecosystems described over recent years. Extreme environmental conditions include hypersalinity, high UV incidence, and high arsenic content, among others. After Socompa’s stromatolite microbial communities were analysed by metagenomic DNA sequencing, taxonomic classification showed dominance of Proteobacteria, Bacteroidetes and Firmicutes, and a remarkably high number of unclassified sequences. A functional analysis indicated that carbon fixation might occur not only by the Calvin-Benson cycle, but also through alternative pathways such as the reverse TCA cycle, and the reductive acetyl-CoA pathway. Deltaproteobacteria were involved both in sulfate reduction and nitrogen fixation. Significant differences were found when comparing the Socompa stromatolite metagenome to the Shark Bay (Australia) smooth mat metagenome: namely, those involving stress related processes, particularly, arsenic resistance. An in-depth analysis revealed a surprisingly diverse metabolism comprising all known types of As resistance and energy generating pathways. While the ars operon was the main mechanism, an important abundance of arsM genes was observed in selected phyla. The data resulting from this work will prove a cornerstone for further studies on this rare microbial community.EEA RafaelaFil: Kurth, Daniel German. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tucumán. Planta Piloto de Procesos Industriales Microbiológicos; ArgentinaFil: Amadio, Ariel F. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Rafaela; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ordoñez, Omar F. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tucumán. Planta Piloto de Procesos Industriales Microbiológicos; ArgentinaFil: Allbarracín, Virginia H. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tucumán. Planta Piloto de Procesos Industriales Microbiológicos; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales. Instituto Miguel Lillo; ArgentinaFil: Farías, María E. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tucumán. Planta Piloto de Procesos Industriales Microbiológicos; ArgentinaFil: Gärtner, Wolfgang. Max-Planck Institute for Chemical Energy Conversion; Alemani

Nuevas aportaciones al conocimiento de los microturbelarios de la Península Ibérica

In this study, seven species of freshwater Microturbellaria are recorded for the first time from the Iberian fauna, belonging to the Orders: Macrostomida (Macrostomum rostratum), Proseriata (Bothrioplana semperi) and Rhabdocoela (Castradella gladiata, Opistomum inmigrans, Phaenocora minima, Microdalyellia kupelweiseri and M. tenennsensis). Other five species are recorded for the second time: Prorhynchus stagnalis (O. Lecithoepitheliata), Opisthocystis goettei, Castrella truncata, Mesostoma ehrenbergii and Rhynchomesostoma rostratum (O. Rhabdocoela). The specimens were collected from eight localities in the provinces of Avila, Cuenca, Guadalajara, Madrid and Segovia. In this report, we bring new data about ecology and distribution of all these species.En el presente trabajo se citan por vez primera para la fauna ibérica siete especies de Microturbelarios pertenecientes a los Órdenes: Macrostomida (Macrostomum rostratum), Proseriata (Bothrioplana semperi) y Rhabdocoela (Castradella gladiata, Opistomum inmigrans, Phaenocora minima, Microdalyellia kupelweiseri y M. tenennsensis). Otras cinco especies se citan por segunda vez: Prorhynchus stagnalis (O. Lecithoepitheliata), Opisthocystis goettei, Castrella truncata, Mesostoma ehrenbergii y Rhynchomesostoma rostratum (O. Rhabdocoela). El material estudiado fue recogido en ocho localidades de las provincias de Avila, Cuenca, Guadalajara, Madrid y Segovia, ofreciéndose nuevos datos sobre la autoecología y distribución de estas especies

Catalytic wet peroxide oxidation of imidazolium-based ionic liquids: Catalyst stability and biodegradability enhancement

This Accepted Manuscript will be available for reuse under a CC BY-NC-ND license after 24 months of embargo periodThe catalytic wet peroxide oxidation (CWPO) of the imidazolium-based ionic liquids 1-butyl-3-methylimidazolium chloride (BmimCl), 1-butyl-3-methylimidazolium acetate (BmimAc), 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BmimNTf2), 1-hexyl-3-methylimidazolium chloride (HmimCl) and 1-decyl-3-methylimidazolium chloride (DmimCl) was examined by using a Fe catalyst supported on alumina (Fe2O3/Al2O3) that was prepared by incipient wetness impregnation. Variable H2O2 doses from 0.5 to 1.5 times the stoichiometric value provided similar results in terms mg TOC removed per mg H2O2 decomposed at 80 °C (0.033 mgTOC mgH2O2−1), all allowing complete Bmim+ removal. Raising the reaction temperature to 90 °C increased the mineralization rate up to 40% TOC conversion. Differences in TOC conversion among counteranions (chloride, acetate and NTf2−) were negligible. A plausible reaction pathway is propose involving hydroxylated compounds and short-chain organic acids as reaction byproducts. CWPO markedly increased the subsequent biodegradability of the IL test solutions and led there to TOC conversions after CWPO-biodegradability assays of 55–60%. The Fe2O3/Al2O3 catalyst exhibited high long-term stability; thus, it retained most of its properties and underwent negligible Fe leaching.The authors acknowledge funding from Spain’s MINECO (CTM2016-76564-R), the Madrid Regional Government (S2013/MAE-2716), UAM-Santander (CEAL-AL/2015-08) and UNAM Engineering Institute (II-4307). I. F. Mena also thanks MINECO and ESF for award of a research gran