Conductance quantization and snake states in graphene magnetic waveguides

We consider electron waveguides (quantum wires) in graphene created by suitable inhomogeneous magnetic fields. The properties of uni-directional snake states are discussed. For a certain magnetic field profile, two spatially separated counter-propagating snake states are formed, leading to conductance quantization insensitive to backscattering by impurities or irregularities of the magnetic field.Comment: 5 pages, 4 figures, final version accepted as Rapid Comm. in PR

Shannon Multiresolution Analysis on the Heisenberg Group

We present a notion of frame multiresolution analysis on the Heisenberg group, abbreviated by FMRA, and study its properties. Using the irreducible representations of this group, we shall define a sinc-type function which is our starting point for obtaining the scaling function. Further, we shall give a concrete example of a wavelet FMRA on the Heisenberg group which is analogous to the Shannon MRA on \RR.Comment: 17 page

Tracing a Route and Finding a Shortcut: The Working Memory, Motivational, and Personality Factors Involved

Wayfinding (WF) is the ability to move around efficiently and find the way from a starting point to a destination. It is a component of spatial navigation, a coordinate and goal-directed movement of one\u2019s self through the environment. In the present study, the relationship between WF tasks (route tracing and shortcut finding) and individual factors were explored with the hypothesis that WF tasks would be predicted by different types of cognitive, affective, motivational variables, and personality factors. A group of 116 university students (88 F.) were conducted along a route in a virtual environment and then asked first to trace the same route again, and then to find a shortcut between the start and end points. Several instruments assessing visuospatial working memory, mental rotation ability, self-efficacy, spatial anxiety, positive attitude to exploring, and personality traits were administered. The results showed that a latent spatial ability factor (measured with the visuospatial working memory and mental rotations tests) \u2013 controlled for gender \u2013 predicted route-tracing performance, while self-report measures of anxiety, efficacy, and pleasure in exploring, and some personality traits were more likely to predict shortcut-finding performance. We concluded that both personality and cognitive abilities affect WF performance, but differently, depending on the requirements of the task

Location models applied to the design of a distribution network for hydrogen fuel produced from renewable energy sources

El agotamiento de las reservas de combustibles fósiles, la creciente preocupación sobre el posible impacto a corto y mediano plazo de las emisiones de gases invernadero en la sociedad y el medio ambiente, y las resultantes políticas orientadas hacia energías más limpias y menor dependencia de combustibles fósiles, han todos puesto mayor presión en incrementar la capacidad de generar energía a partir de fuentes renovables, de las cuales la energía eólica ha sido uno de los segmentos de más rápido desarrollo. Sin embargo, la naturaleza intermitente e impredecible de estas fuentes, combinada con las limitaciones de la actual infraestructura de transmisión, se traduce en una cantidad significativa de energía eólica desperdiciada y en que no se llegue a explotar adecuadamente la capacidad instalada de generación. El hidrógeno ha sido identificado como un vector energético limpio para almacenar la energía producida a partir de dichas fuentes variables. Adicionalmente, el hidrógeno ha demostrado su factibilidad como combustible de cero emisiones para uso en transporte, sea a través de sistemas de combustión o celdas de combustible. El uso del hidrógeno como mecanismo de almacenaje puede ayudar a absorber las fluctuaciones en el suministro de energía, y potencialmente aumentar la utilización de la capacidad disponible de generación renovable. El desarrollo de una infraestructura de producción y distribución de hidrógeno es un tema de gran relevancia en la evaluación de la viabilidad a largo plazo de este vector energético. Esta tesis doctoral se centra en las decisiones enfrentadas por una empresa con capacidad de generación de energía renovable, cuando también le es posible producir hidrógeno por medio de electrólisis conectada a la red. Primero nos enfocamos en las decisiones de diseño de la cadena de suministro para el productor; específicamente, dónde localizar las instalaciones de producción de hidrógeno, cuánta capacidad construir en cada instalación, y cuánto hidrógeno debe ser distribuido a instancias posteriores en la red. Presentamos una serie de modelos de optimización para el diseño de la red de producción y distribución, considerando el valor adicional creado por la producción de hidrógeno para una empresa generadora, incorporando la incertidumbre en el suministro de energía renovable y en los precios de electricidad. La empresa opera en un mercado regulado por una agencia externa con la capacidad de fijar precios para el combustible de hidrógeno y establecer políticas generales de servicio para el mercado siendo considerado por el productor. Los Capítulos 2 y 3 de la tesis están enfocados en la problemática del productor bajo dos políticas regulatorias de distribución: selección de mercados y asignación proporcional. Para abordar este problema presentamos procedimientos de solución basados en métodos de generación de columnas. A manera de fundamentar nuestro trabajo en un contexto práctico, en el Capítulo 4 implementamos nuestros modelos para evaluar una futura red de combustible de hidrógeno en España, y evaluamos el efecto de los incentivos externos (subsidios) sobre las decisiones del productor, permitiéndonos ganar intuición sobre cómo dichos incentivos pueden ser puestos en marcha para hacer viable una economía de hidrógeno

Tomonaga-Luttinger liquid parameters of magnetic waveguides in graphene

Electronic waveguides in graphene formed by counterpropagating snake states in suitable inhomogeneous magnetic fields are shown to constitute a realization of a Tomonaga-Luttinger liquid. Due to the spatial separation of the right- and left-moving snake states, this non-Fermi liquid state induced by electron-electron interactions is essentially unaffected by disorder. We calculate the interaction parameters accounting for the absence of Galilei invariance in this system, and thereby demonstrate that non-Fermi liquid effects are significant and tunable in realistic geometries

Nitrosamine exposure exacerbates high fat diet-mediated type 2 diabetes mellitus, non-alcoholic steatohepatitis, and neurodegeneration with cognitive impairment

BACKGROUND: The current epidemics of type 2 diabetes mellitus (T2DM), non-alcoholic steatohepatitis (NASH), and Alzheimer's disease (AD) all represent insulin-resistance diseases. Previous studies linked insulin resistance diseases to high fat diets or exposure to streptozotocin, a nitrosamine-related compound that causes T2DM, NASH, and AD-type neurodegeneration. We hypothesize that low-level exposure to nitrosamines that are widely present in processed foods, amplifies the deleterious effects of high fat intake in promoting T2DM, NASH, and neurodegeneration. METHODS: Long Evans rat pups were treated with N-nitrosodiethylamine (NDEA) by i.p. Injection, and upon weaning, they were fed with high fat (60%; HFD) or low fat (5%; LFD) chow for 6 weeks. Rats were evaluated for cognitive impairment, insulin resistance, and neurodegeneration using behavioral, biochemical, molecular, and histological methods. RESULTS: NDEA and HFD +/- NDEA caused T2DM, NASH, deficits in spatial learning, and neurodegeneration with hepatic and brain insulin and/or IGF resistance, and reductions in tau and choline acetyltransferase levels in the temporal lobe. In addition, pro-ceramide genes, which promote insulin resistance, were increased in livers and brains of rats exposed to NDEA, HFD, or both. In nearly all assays, the adverse effects of HFD+NDEA were worse than either treatment alone. CONCLUSIONS: Environmental and food contaminant exposures to low, sub-mutagenic levels of nitrosamines, together with chronic HFD feeding, function synergistically to promote major insulin resistance diseases including T2DM, NASH, and AD-type neurodegeneration. Steps to minimize human exposure to nitrosamines and consumption of high-fat content foods are needed to quell these costly and devastating epidemics

Short and user-friendly: The development and validation of the Mini-DBQ

The Driver Behavior Questionnaire (DBQ) is used to measure aberrant driver behavior by asking drivers how often they engage in various aberrant driver behaviors. Since the development of the original DBQ several modified versions have been developed. The difference between the various versions is that new items are added or existing items modified or excluded. However, despite the differences, all versions are relatively long and therefore time-consuming and tiring to answer, which might limit the usability of the instrument. The main purpose of the present study was to develop a mini DBQ version by reducing the 27-item original DBQ to the shortest possible DBQ version. A second aim was to explore the feasibility of a second-order structure within the data, which means that violations, errors and lapses factors load on a higher-order aberrant driver behavior factor. The presence of a second-order structure further indicates the validity of the DBQ and its theoretical structure. Confirmatory factor analysis (CFA) was used to test the fit (i.e., how well the models explain the data) of the original DBQ versus the fit of the shortest possible DBQ as well as the presence of a second-order structure for the DBQ. The results indicated a nine-item Mini-DBQ In addition, a second-order structure was established in the data. These findings indicate that the Mini-DBQ is a valid and useful short measure of aberrant driver behavior

Aspartyl-(asparaginyl) β-Hydroxylase, Hypoxia-Inducible Factor-1α and Notch Cross-Talk in Regulating Neuronal Motility

Aspartyl-(Asparaginyl)-β-Hydroxylase (AAH ) promotes cell motility by hydroxylating Notch. Insulin and insulin-like growth factor, type 1 (IGF-I) stimulate AAH through Erk MAP K and phosphoinositol-3-kinase-Akt (PI3K-Akt). However, hypoxia/oxidative stress may also regulate AAH . Hypoxia-inducible factor-1alpha (HIF-1α) regulates cell migration, signals through Notch, and is regulated by hypoxia/oxidative stress, insulin/IGF signaling and factor inhibiting HIF-1α (FIH) hydroxylation. To examine cross-talk between HIF-1α and AAH , we measured AAH , Notch-1, Jagged-1, FIH, HIF-1α, HIF-1β and the hairy and enhancer of split 1 (HE S-1) transcription factor expression and directional motility in primitive neuroectodermal tumor 2 (PNET2) human neuronal cells that were exposed to H2O2 or transfected with short interfering RNA duplexes (siRNA) targeting AAH , Notch-1 or HIF-1α. We found that: (1) AAH , HIF-1α and neuronal migration were stimulated by H2O2; (2) si-HIF-1α reduced AAH expression and cell motility; (3) si-AAH inhibited Notch and cell migration, but not HIF-1α and (4) si-Notch-1 increased FIH and inhibited HIF-1α. These findings suggest that AAH and HIF-1α crosstalk within a hydroxylation-regulated signaling pathway that may be transiently driven by oxidative stress and chronically regulated by insulin/IGF signaling

Discrete radar ambiguity problems

In this paper, we pursue the study of the radar ambiguity problem started in \cite{Ja,GJP}. More precisely, for a given function $u$ we ask for all functions $v$ (called \emph{ambiguity partners}) such that the ambiguity functions of $u$ and $v$ have same modulus. In some cases, $v$ may be given by some elementary transformation of $u$ and is then called a \emph{trivial partner} of $u$ otherwise we call it a \emph{strange partner}. Our focus here is on two discrete versions of the problem. For the first one, we restrict the problem to functions $u$ of the Hermite class, $u=P(x)e^{-x^2/2}$, thus reducing it to an algebraic problem on polynomials. Up to some mild restriction satisfied by quasi-all and almost-all polynomials, we show that such a function has only trivial partners. The second discretization, restricting the problem to pulse type signals, reduces to a combinatorial problem on matrices of a special form. We then exploit this to obtain new examples of functions that have only trivial partners. In particular, we show that most pulse type signals have only trivial partners. Finally, we clarify the notion of \emph{trivial partner}, showing that most previous counterexamples are still trivial in some restricted sense