Quantum nanoconstrictions fabricated by cryo-etching in encapsulated graphene

More than a decade after the discovery of graphene, ballistic transport in nanostructures based on this intriguing material still represents a challenging field of research in two-dimensional electronics. The presence of rough edges in nanostructures based on this material prevents the appearance of truly ballistic electron transport as theo\-re\-tically predicted and, therefore, not well-developed plateaus of conductance have been revealed to date. In this work we report on a novel implementation of the cryo-etching method, which enabled us to fabricate graphene nanoconstrictions encapsulated between hexagonal boron nitride thin films with unprecedented control of the structure edges. High quality smooth nanometer-rough edges are characterized by atomic force microscopy and a clear correlation between low roughness and the existence of well-developed quantized conductance steps with the concomitant occurrence of ballistic transport is found at low temperature. In par\-ti\-cu\-lar, we come upon exact 2$e^{2}/h$ quantization steps of conductance at zero magnetic field due to size quantization, as it has been theoretically predicted for truly ballistic electron transport through graphene nanoconstrictions

Thermochemistry of uracil and thymine revisited

© 2015 Published by Elsevier Ltd. Thermochemical properties of uracil and thymine have been evaluated using additional experiments. Standard (p0 = 0.1 MPa) molar enthalpies of formation in the gas phase at T = 298.15 K for uracil -(298.1 ± 0.6) and for thymine -(337.6 ± 0.9) kJ · mol-1 have been derived from energies of combustion measured by static bomb combustion calorimetry and molar enthalpies of sublimation determined using the transpiration method. The G3 and G4 quantum-chemical methods were used for calculations of theoretical gaseous enthalpies of formation being in very good agreement with the re-measured experimental values

Convergent validity of two items to differentiate between active and sedentary students

Este estudio examina la validez y fiabilidad de dos ítems de actividad física (AF) incluidos en el CHIP-CE para discriminar entre escolares activos y sedentarios. Se realizó un estudio observacional-transversal, con 1.073 escolares de ambos sexos, de 10-13 años. Mediante los ítems 13 y 28 del CHIP-CE se clasificó a los escolares como activos o sedentarios. La validez convergente fue examinada utilizando como criterio variables de adiposidad, lipídicas, metabólicas, de presión arterial y de fitness. El coeficiente de correlación de Spearman entre los dos ítems fue de 0,60. Los coeficientes de correlación de Spearman entre la media de los dos items de AF y las variables de salud mostraron valores más altos con el % grasa corporal, la insulina basal, la frecuencia cardiaca de recuperación y el fitness. La escala de dos ítems extraída del CHIP-CE es un instrumento válido para clasificar a los escolares en activos o sedentarios.This study examined the validity and reliability of two physical activity Child Health and Illness Profile - Child Edition (CHIP-CE) items to differentiate between active and sedentary students. An observational cross-sectional study design was used with 1,073 students from 11 to 13 years old, from 20 schools in the province of Cuenca (Spain). Item 13 and item 28 of the CHIP-CE, a generic childhood quality of life instrument, were evaluated. Convergent validity was examined using adiposity, lipidic, metabolic, blood pressure and cardiorespiratory fitness variables as criteria. The Spearman coefficient of correlation between the two items was 0.60. The Spearman correlation coefficients between the physical activity items and the anthropometric, lipidic, metabolic, blood pressure and cardiorespiratory fitness variables showed higher values with percentage body fat, fasting insulin, recovery heart rate and cardiorespiratory fitness. Our two-item questionnaire exhibited acceptable validity and high internal consistency for classifying students as either active or sedentary.Este estudio fue financiado por la Consejería de Sanidad de Castilla-La Mancha (beca GC03060-00). Financiación adicional fue obtenida del Ministerio de Sanidad y Consumo, Instituto de Salud Carlos III, Red de Investigación en Actividades Preventivas y de Promoción de Salud (grant RD06/0018/0038)

Physical activity and bone health in schoolchildren: the mediating role of fitness and body fat

This is the final version of the article. Available from Public Library of Science via the DOI in this record.BACKGROUND: The relationship between physical activity (PA) and bone health is well known, although the role of percent body fat (%BF) and fitness as confounders or mediators in this relationship remains uncertain. OBJECTIVE: To examine whether the association between PA and bone mineral content (BMC) is mediated by %BF and cardiorespiratory fitness (CRF). METHODS: In this cross sectional study, BMC, total %BF (by DXA), vigorous PA (VPA), CRF, age and height were measured in 132 schoolchildren (62 boys, aged 8-11 years). ANCOVA was used to test differences in BMC by %BF, CRF and VPA, controlling for different sets of confounders. Simple mediation analyses and serial multiple mediation analyses were fitted to examine whether the relationship between PA and BMC is mediated by %BF and fitness. RESULTS: Children with high %BF had higher total body BMC than their peers after controlling for all sets of confounders. Children with good CRF or VPA had significantly less total body BMC after controlling for age and sex but in children with good CRF this inverse relation disappeared after adjusting by %BF. %BF and CRF both act as a full mediator in the association between VPA and BMC, after inclusion of the potential confounders in the models. CONCLUSION: Fitness and %BF seem to have a mediator role on the relationship between physical activity and bone mass.This study was funded by grant numbers PII1I09-0259-9898 and POII10-0208-5325 from the Ministry of Education and Science - Junta de Comunidades de Castilla-La Mancha, and Ministry of Health (FIS grant number PI081297). Additional funding was provided by the Research Network on Preventative Activities and Health Promotion (RD06/0018/0038)

El Instituto Español de Entomología (CSIC) y la multitud molesta

The Spanish Institute of Entomology (IEE) was founded in 1941, direct heir of the former Entomology Section of the National Museum of Natural Science. Among the tasks assigned to the new Institute was to provide “to the interested centers the data resulting from the work that he made with insects with economic and public health significance”. Gonzalo Ceballos was appointed Director; his proposals, alongside the work of the institutions responsible for forest management, turned up the IEE into one of the driving forces of many initiatives in this field. His management also provided an excellent opportunity to meet the objectives for which the Institute was conceived. Three forms of participation were distinguished on the study, management and control of forest pests. On one hand, the involvement of the IEE in resolving queries from individuals, companies and institutions; second, the development of scientific projects supported by the Juan de la Cierva Board of Trustees and, finally, collaborations with different departments belonging of the Ministry of Agriculture. It is stated that, the lack of specialized personnel assigned to the IEE pests’ management was a serious drawback to continue the initiatives of Ceballos be developed beyond management.En 1941 se creó el Instituto Español de Entomología (IEE), heredero directo de la antigua Sección de Entomología del Museo Nacional de Ciencias Naturales. Entre las labores encomendadas al nuevo establecimiento estaba la de aportar «a los Centros de aplicación los datos resultantes de los trabajos que en él se efectúen con los insectos, de interés económico y sanitario». Gonzalo Ceballos fue nombrado Director y sus propuestas, junto al trabajo de las instituciones encargadas de la gestión forestal, hicieron del IEE uno de los centros motores de muchas iniciativas en este campo. Su dirección supuso, además, una excelente oportunidad para cumplir los objetivos con los que fue concebido el Instituto. En este artículo se distinguen tres formas de participación respecto al estudio, gestión y control de plagas forestales. Por un lado, la implicación del IEE en la resolución de consultas de particulares, empresas e instituciones; en segundo lugar, el desarrollo de proyectos subvencionados por el Patronato Juan de la Cierva y, finalmente, las colaboraciones con diferentes cuerpos dependientes del Ministerio de Agricultura. Se constata que la falta de personal especializado en plagas adscrito al IEE supuso un grave inconveniente para que las iniciativas de Ceballos se desarrollaran más allá de su gestión

Identification of Pigment Epithelium-Derived Factor Protein Forms with Distinct Activities on Tumor Cell Lines

Purpose. Pigment epithelium-derived factor (PEDF) is a multifunctional serpin. The purpose of this study is to identify PEDF protein forms and investigate their biological activities on tumor cell lines. Methods. Recombinant human PEDF proteins were purified by cation- and anion-exchange column chromatography. They were subjected to SDS-PAGE, IEF, deglycosylation, heparin affinity chromatography, and limited proteolysis. Cell viability, real-time electrical impedance of cells, and wound healing assays were performed using bladder and breast cancer cell lines, rat retinal R28, and human ARPE-19 cells. Results. Two PEDF protein peaks were identified after anion-exchange column chromatography: PEDF-1 eluting with lower ionic strength than PEDF-2. PEDF-1 had higher pI value and lower apparent molecular weight than PEDF-2. Both PEDF forms were glycosylated, bound to heparin, and had identical patterns by limited proteolysis. However, PEDF-2 emerged as being highly potent in lowering cell viability in all tumor cell lines tested, and in inhibiting tumor and ARPE-19 cell migration. In contrast, PEDF-1 minimally affected tumor cell viability and cell migration but protected R28 cells against death caused by serum starvation. Conclusion. Two distinct biochemical forms of PEDF varying in overall charge have distinct biological effects on tumor cell viability and migration. The existence of PEDF forms may explain the multifunctional modality of PEDF

Thermochemistry of 1,3-diethylbarbituric and 1,3-diethyl-2-thiobarbituric acids: Experimental and computational study

This paper reports an experimental and computational thermochemical study on two barbituric acid derivatives, viz. 1,3-diethylbarbituric acid and 1,3-diethyl-2-thiobarbituric acid. Values of standard molar enthalpies of formation in the gas phase at T = 298.15 K have been derived from experiment. Energies of combustion were measured by the static bomb combustion calorimetry in the case of 1,3-diethylbarbituric acid, and the rotating-bomb combustion calorimetry in the case of 1,3-diethyl-2-thiobarbituric acid. From the combustion energies, standard molar enthalpies of formation in the crystalline state at T = 298.15 K were calculated. The enthalpy of vaporization of 1,3-diethylbarbituric acid and enthalpy of sublimation of 1,3-diethyl-2- thiobarbituric acid were determined using the transpiration method. Combining calorimetric and transpiration results, values of -(611.9 ± 2.0) kJ · mol-1 and -(343.8 ± 2.2) kJ·mol-1 for the gas-phase enthalpies of formation at T = 298.15 K of 1,3-diethylbarbituric and 1,3-diethyl-2-thiobarbituric acids, respectively, were derived. Theoretical calculations at the G3 and G4 levels were performed, and a study of the molecular structure of the compounds has been carried out. Calculated enthalpies of formation were in very good agreement with the experimental values. © 2014 Elsevier Ltd. All rights reserved

Mechanical Properties of PMMA-Sepiolite Nanocellular Materials with a Bimodal Cellular Structure

Bimodal cellular poly(methyl methacrylate) with micron and nano sized (300 to 500 nm) cells with up to 5 weight percent of sepiolite nanoparticles and porosity from 50 weight percent to 75 weight percent are produced by solid state foaming. Uniaxial compression tests are performed to measure the effect of sepiolite concentration on the elastic modulus and the yield strength of the solid and cellular nanocomposites. Single edge notch bend tests are conducted to relate the fracture toughness of the solid and cellular nanocomposites to sepiolite concentration. The relative modulus is independent of sepiolite content to within material scatter when considering the complete porosity range. In contrast, a mild enhancement of the relative modulus is observed by the addition of sepiolite particles for the foamed nanocomposites with a porosity close to 50 percent. The relative compressive strength of the cellular nanocomposites mildly decreases as a function of sepiolite concentration. A strong enhancement of the relative fracture toughness by the addition of sepiolites is observed. The enhancement of the relative fracture toughness and the relative modulus (at 50 percent porosity) can be attributed to an improved dispersion of the particles due to foaming and the migration of micron sized aggregates from the solid phase to the microcellular pores during foaming

Experimental and theoretical study of the structures and enthalpies of formation of the synthetic reagents l,3-thiazolidine-2-thione and l,3-oxazolidine-2-thione

This paper reports an experimental and a theoretical study of the structures and standard (po = 0.1 MPa) molar enthalpies of formation of the synthetic reagents 1,3-thiazolidine-2-thione [CAS 96-53-7] and 1,3-oxazolidine-2-thione [CAS 5840-81-3]. The enthalpies of combustion and sublimation were measured by rotary bomb combustion calorimetry, and the Knudsen effusion technique and gas-phase enthalpies of formation values at T = 298.15 K of (97.1 ± 4.0) and −(74.4 ± 4.6) kJ·mol−1 for 1,3-thiazolidine-2-thione and 1,3-oxazolidine-2-thione, respectively, were determined. G3-calculated enthalpies of formation are in reasonable agreement with the experimental values. In the solid state, 1,3-thiazolidine-2-thione exists in two polymorphic forms (monoclinic and triclinic) and 1,3-oxazolidine-2-thione exits in the triclinic form. The isostructural nature of these compounds and comparison of their molecular and crystal structures have been analyzed. The experimental X-ray powder diffractograms have been compared with the calculated patterns from their structures for identification of the polymorphic samples used in this study. A comparison of our results with literature thermochemical and structural data for related compounds is also reported.M.T. would like to thank MEC/SEUI, FPU AP2002-0603, Spain, for financial support. A.V.D. thanks the National Science Foundation (CHE-0547566) and the American Heart Association (0855743G) for financial support of this research. The support of the Spanish Ministerio de Educación y Ciencia under Projects CTQ2007-60895/BQU and CTQ2006-10178/BQU is gratefully acknowledged