Spin-dependent THz oscillator based on hybrid graphene superlattices

We theoretically study the occurrence of Bloch oscillations in biased hybrid graphene systems with spin-dependent superlattices. The spin-dependent potential is realized by a set of ferromagnetic insulator strips deposited on top of a gapped graphene nanoribbon, which induce a proximity exchange splitting of the electronic states in the graphene monolayer. We numerically solve the Dirac equation and study Bloch oscillations in the lowest conduction band of the spin-dependent superlattice. While the Bloch frequency is the same for both spins, we find the Bloch amplitude to be spin dependent. This difference results in a spin-polarized ac electric current in the THz range.Comment: 4 pages, 6 figure

Estimating causal networks in biosphere–atmosphere interaction with the PCMCI approach

Local meteorological conditions and biospheric activity are tightly coupled. Understanding these links is an essential prerequisite for predicting the Earth system under climate change conditions. However, many empirical studies on the interaction between the biosphere and the atmosphere are based on correlative approaches that are not able to deduce causal paths, and only very few studies apply causal discovery methods. Here, we use a recently proposed causal graph discovery algorithm, which aims to reconstruct the causal dependency structure underlying a set of time series. We explore the potential of this method to infer temporal dependencies in biosphere-atmosphere interactions. Specifically we address the following questions: How do periodicity and heteroscedasticity influence causal detection rates, i.e. the detection of existing and non-existing links? How consistent are results for noise-contaminated data? Do results exhibit an increased information content that justifies the use of this causal-inference method? We explore the first question using artificial time series with well known dependencies that mimic real-world biosphere-atmosphere interactions. The two remaining questions are addressed jointly in two case studies utilizing observational data. Firstly, we analyse three replicated eddy covariance datasets from a Mediterranean ecosystem at half hourly time resolution allowing us to understand the impact of measurement uncertainties. Secondly, we analyse global NDVI time series (GIMMS 3g) along with gridded climate data to study large-scale climatic drivers of vegetation greenness. Overall, the results confirm the capacity of the causal discovery method to extract time-lagged linear dependencies under realistic settings. The violation of the method's assumptions increases the likelihood to detect false links. Nevertheless, we consistently identify interaction patterns in observational data. Our findings suggest that estimating a directed biosphere-atmosphere network at the ecosystem level can offer novel possibilities to unravel complex multi-directional interactions. Other than classical correlative approaches, our findings are constrained to a few meaningful set of relations which can be powerful insights for the evaluation of terrestrial ecosystem models

Simple heuristics for the assembly line worker assignment and balancing problem

We propose simple heuristics for the assembly line worker assignment and balancing problem. This problem typically occurs in assembly lines in sheltered work centers for the disabled. Different from the classical simple assembly line balancing problem, the task execution times vary according to the assigned worker. We develop a constructive heuristic framework based on task and worker priority rules defining the order in which the tasks and workers should be assigned to the workstations. We present a number of such rules and compare their performance across three possible uses: as a stand-alone method, as an initial solution generator for meta-heuristics, and as a decoder for a hybrid genetic algorithm. Our results show that the heuristics are fast, they obtain good results as a stand-alone method and are efficient when used as a initial solution generator or as a solution decoder within more elaborate approaches.Comment: 18 pages, 1 figur

Revisión de los Gordiacea (Nematomorpha) de la colección de la Academia de Ciencias de California con descripción de una nueva especie

The Gordiacea of the California Academy of Sciences collection are studied. The specimens are included in the known species Gordius robustus Leidy, Pseudochordodes bedriagae (Camerano) and a new species, Neochordodes californensis n. sp. is proposed. Morphological, morphometric and geographical data are provided for these species.En este trabajo se estudian los Gordiacea de la colección de la California Academy of Sciences. Los ejemplares se incluyen en dos especies conocidas, Gordius robustus Leidy y Pseudochordodes bedriagae (Camerano), y una especie nueva: Neochordodes californensis n. sp. Se proporcionan datos morfológicos, morfométricos y geográficos para cada una de las especies

Z_2-gradings of Clifford algebras and multivector structures

Let Cl(V,g) be the real Clifford algebra associated to the real vector space V, endowed with a nondegenerate metric g. In this paper, we study the class of Z_2-gradings of Cl(V,g) which are somehow compatible with the multivector structure of the Grassmann algebra over V. A complete characterization for such Z_2-gradings is obtained by classifying all the even subalgebras coming from them. An expression relating such subalgebras to the usual even part of Cl(V,g) is also obtained. Finally, we employ this framework to define spinor spaces, and to parametrize all the possible signature changes on Cl(V,g) by Z_2-gradings of this algebra.Comment: 10 pages, LaTeX; v2 accepted for publication in J. Phys.

Fracturas supracondíleas de fémur tratadas con clavo retrógrado versus tornillo condilar dinámico

Objetivo: valorar los resultados mediante tratamiento con clavo intramedular retrógrado (CIR). Material y Métodos: se revisaron 54 pacientes con fracturas supracondíleas de fémur tipos AO A y C1, con edad media de 68 años, de los que 23 fueron tratados con CIR y 31 con tornillo condilar dinámico (TCD). Seguimiento medio de 5 años (rango, 2 a 9). Se valoraron clínicamente con las escalas Knee Society y cuestionario Womac y radiográficamente. Resultados: no hubo diferencias significativas respecto a los datos perioperatorios, resultados funcionales, movilidad de rodilla, calidad de vida o tiempo medio de consolidación. En el grupo CIR no hubo pseudoartrosis y 2 pacientes tuvieron acortamiento mayor de 2 cm. En el grupo TCD hubo 2 pseudoartrosis que precisaron reintervención y otros 4 casos tuvieron consolidación con desviación angular de al menos 5º, 2 de ellos además con acortamiento mayor de 2 cm. Discusión: los resultados fueron similares en ambos grupos pero, aunque no significativamente, con el CIR hubo menor número de complicaciones de alineación y de consolidación. Conclusiones: el CIR es un método satisfactorio para las fracturas supracondíleas sin o poca afectación articular, tanto en jóvenes como en ancianos.Objective: To evaluate functional and radiographic results after retrograde intramedullary nail (RIN). Material and Methods: We reviewed 54 supracondylar femoral fractures, AO-types A and C1, in patients with mean aged of 68 years, of which 23 were treated with RIN and 31 with dynamic condylar screw (DCS). Mean follow-up of 5 years (range, 2 to 9). They were evaluated clinically by means Knee Society scores and Womac self-form, and radiographically. Results: There were no significant differences with reagard to perioperative data, functional results, knee mobility, quality of life, or mean healed time. In the RIN group, there was no nonunion, and 2 patients had shortening greater than 2cm. In the DCS group, there were 2 nonunion which required revision, and other 4 healed with angular malunion greater than 5º, 2 of which had also shortening greater than 2cm. Discussion: Outcomes were similar in both groups. Although no significantly, the RIN group had lower malunion and nonunion rates. Conclusion: RIN is a satisfactory method for supracondylar fractures with little or no joint involvement, for both young and elderly patients

Post-Coronal Mass Ejection Plasma Observed by Hinode

In the present work we study the evolution of an active region after the eruption of a coronal mass ejection (CME) using observations from the EIS and XRT instruments on board Hinode . The field of view includes a post-eruption arcade, a current sheet, and a coronal dimming. The goal of this paper is to provide a comprehensive set of measurements for all these aspects of the CME phenomenon made on the same CME event. The main physical properties of the plasma along the line of sight—electron density, thermal structure, plasma composition, size, and, when possible, mass—are measured and monitored with time for the first three hours following the CME event of 2008 April 9. We find that the loop arcade observed by EIS and XRT may not be related to the post-eruption arcade. Post-CME plasma is hotter than the surrounding corona, but its temperature never exceeds 3 MK. Both the electron density and thermal structure do not show significant evolution with time, while we found that the size of the loop arcade in the Hinode plane of the sky decreased with time. The plasma composition is the same in the current sheet, in the loop arcade, and in the ambient plasma, so all these plasmas are likely of coronal origin. No significant plasma flows were detected.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98557/1/0004-637X_751_1_21.pd

Naturalness and the Hierarchy Problem in the type I and type II See-Saw Models

In this thesis, the type I and type II see-saw models are considered separately as the mechanism to generate small neutrino masses and the radiative corrections to the Higgs mass induced by these models are studied. Especially, the influence of imposing naturalness is tested. As the naturalness criterion, it is assumed that quantum corrections should not be larger than the Higgs mass. Imposing this condition, limits on the new mass scale introduced in each model can be set, so that no hierarchy problem arises. For the type I, it is found that the mass of the right-handed neutrino could take values up to O(107 GeV) without generating large corrections. For the type II, the parameter space of the extended scalar potential is first restricted by imposing vacuum stability, unitarity of scattering processes and experimental constraints, before testing the influence of imposing naturalness. Only small values of the triplet vacuum expectation value, O(eV), which give rise to sizeable Yukawa couplings, are considered. In this scenario, there exist a large parameter space satisfying the vacuum stability, unitarity and experimental constraints. Of this parameter space, all sets of parameters satisfy the naturalness condition for triplet masses below 1 TeV and a large subset satisfies naturalness for masses between 1 TeV and 3 TeV. If the triplet mass were located in this energy range, as preferred by naturalness, new particles corresponding to the triplet might be detectable at the Large Hadron Collider or future colliders and also lead to significant signals in lepton flavour violation experiments