Impact of edge shape on the functionalities of graphene-based single-molecule electronics devices

We present an ab-initio analysis of the impact of edge shape and graphene-molecule anchor coupling on the electronic and transport functionalities of graphene-based molecular electronics devices. We analyze how Fano-like resonances, spin filtering and negative differential resistance effects may or may not arise by modifying suitably the edge shapes and the terminating groups of simple organic molecules. We show that the spin filtering effect is a consequence of the magnetic behavior of zigzag-terminated edges, which is enhanced by furnishing these with a wedge shape. The negative differential resistance effect is originated by the presence of two degenerate electronic states localized at each of the atoms coupling the molecule to graphene which are strongly affected by a bias voltage. The effect could thus be tailored by a suitable choice of the molecule and contact atoms if edge shape could be controlled with atomic precision.Comment: 11 pages, 20 figure

Semiclassical time--dependent propagation in three dimensions: How accurate is it for a Coulomb potential?

A unified semiclassical time propagator is used to calculate the semiclassical time-correlation function in three cartesian dimensions for a particle moving in an attractive Coulomb potential. It is demonstrated that under these conditions the singularity of the potential does not cause any difficulties and the Coulomb interaction can be treated as any other non-singular potential. Moreover, by virtue of our three-dimensional calculation, we can explain the discrepancies between previous semiclassical and quantum results obtained for the one-dimensional radial Coulomb problem.Comment: 8 pages, 4 figures (EPS

Solar polarimetry through the K I lines at 770 nm

We characterize the K I D1 & D2 lines in order to determine whether they could complement the 850 nm window, containing the Ca II infrared triplet lines and several Zeeman sensitive photospheric lines, that was studied previously. We investigate the effect of partial redistribution on the intensity profiles, their sensitivity to changes in different atmospheric parameters, and the spatial distribution of Zeeman polarization signals employing a realistic magnetohydrodynamic simulation. The results show that these lines form in the upper photosphere at around 500 km and that they are sensitive to the line of sight velocity and magnetic field strength at heights where neither the photospheric lines nor the Ca II infrared lines are. However, at the same time, we found that their sensitivity to the temperature essentially comes from the photosphere. Then, we conclude that the K I lines provide a complement to the lines in the 850 nm window for the determination of atmospheric parameters in the upper photosphere, especially for the line of sight velocity and the magnetic field.Comment: 10 pages, 9 figures, main journal publicatio

Maternal Risk Factors for Small-for-Gestational-Age Newborns in Mexico: Analysis of a Nationwide Representative Cohort

Background: Small for gestational age (SGA) is a key contributor to premature deaths and long-term complications in life. Improved characterization of maternal risk factors associated with this adverse outcome is needed to inform the development of interventions, track progress, and reduce the disease burden. This study aimed to identify socioeconomic, demographic, and clinical factors associated with SGA in Mexico. Methods: We analyzed administrative data from 1,841,477 singletons collected by the National Information Subsystem of Livebirths during 2017. Small-for-gestational-age was defined as being 12 years (aOR 0.63; 95% CI:0.6,0.66) compared with those without education. SGA was particularly likely to occur among primiparous (aOR 1.42; 95% CI: 1.39, 1.43), mothers living in very high deprivation localities (aOR 1.39; 95% CI: 1.36, 1.43), young (aOR 1.04; 95% CI: 1.02, 1.06), advanced age (aOR 1.14; 95% CI 1.09, 1.19), and mothers living in areas above 2,000 m (aOR 1.69; 95% CI: 1.65, 1.73). Antenatal care was associated with a reduced risk of SGA by 30% (aOR 0.7; 95% CI:0.67,0.73), 23% (OR 0.77; 95% CI:0.74,0.8), and 21% (OR 0.79; 95% CI:0.75,0.83), compared with those mothers who never received antenatal care, when women visited the clinic at the first, second and third trimester, respectively. Conclusion: Almost 7% of live births were found to be SGA. Parity, maternal age, education, place of residence, and social deprivation were significantly associated with this outcome. Antenatal care was protective. These findings imply that interventions focusing on early and adequate contact with health care facilities, reproductive health counseling, and maternal education should reduce SGA in Mexico

Study of the polarization produced by the Zeeman effect in the solar Mg I b lines

The next generation of solar observatories aim to understand the magnetism of the solar chromosphere. Therefore, it is crucial to understand the polarimetric signatures of chromospheric spectral lines. For this purpose, we here examine the suitability of the three Fraunhofer Mg I b1, b2, and b4 lines at 5183.6, 5172.7, and 5167.3 A, respectively. We start by describing a simplified atomic model of only 6 levels and 3 line transitions for computing the atomic populations of the 3p-4s (multiplet number 2) levels involved in the Mg I b line transitions assuming non-local thermodynamic conditions and considering only the Zeeman effect using the field-free approximation. We test this simplified atom against more complex ones finding that, although there are differences in the computed profiles, they are small compared with the advantages provided by the simple atom in terms of speed and robustness. After comparing the three Mg I lines, we conclude that the most capable one is the b2 line as b1 forms at similar heights and always show weaker polarization signals while b4 is severely blended with photospheric lines. We also compare Mg I b2 with the K I D1 and Ca II 8542 A lines finding that the former is sensitive to the atmospheric parameters at heights that are in between those covered by the latter two lines. This makes Mg I b2 an excellent candidate for future multi-line observations that aim to seamlessly infer the thermal and magnetic properties of different features in the lower solar atmosphere.Comment: 14 pages, 11 figures, and 5 table

Diseño, elaboración e implementación de una unidad didáctica de educación ambiental : la formación teórica a luz de la práctica

A través de este trabajo presentamos una experiencia de educación ambiental que reúne la formación de profesores universitarios de biología y de profesores de primaria. La experiencia surge a partir de haber detectado una problemática de enseñanza en la escuela primaria que se intenta revertir a través de las acciones a desarrollar en el contexto de la formación inicial de ambos profesorados, en el ámbito de las asignaturas cuyo desarrollo curricular se centra en la formación teórica de la didáctica de las ciencias. Generamos acciones que nos permitan evaluar cómo influye la formación teórica en el diseño, elaboración e implementación de unidades didácticas en las aulas de la formación de maestros. Luego a través de su transposición didáctica a las aulas de primaria se retroalimenta la formación teórica en didáctica de las ciencias de los profesorados

Berezin Quantization of Gauged WZW and Coset Models

Gauged WZW and coset models are known to be useful to prove holomorphic factorization of the partition function of WZW and coset models. In this note we show that these gauged models can be also important to quantize the theory in the context of the Berezin formalism. For gauged coset models Berezin quantization procedure also admits a further holomorphic factorization in the complex structure of the moduli space.Comment: 15+1 pages, no figures, revte