Fermi pockets and correlation effects in underdoped YBa2Cu3O6.5

The detection of quantum oscillations in the electrical resistivity of YBa2Cu3O6.5 provides direct evidence for the existence of Fermi surface pockets in an underdoped cuprate. We present a theoretical study of the electronic structure of YBa2Cu3O7-d (YBCO) aiming at establishing the nature of these Fermi pockets, i.e. CuO2 plane versus CuO chain or BaO. We argue that electron correlation effects, such as orbital-dependent band distortions and highly anisotropic self-energy corrections, must be taken into account in order to properly interpret the quantum oscillation experiments.Comment: A high-resolution version can be found at http://www.physics.ubc.ca/~quantmat/ARPES/PUBLICATIONS/Articles/YBCO_OrthoII_LDA.pd

The implementation and characterization of electron transfer dissociation (ETD) on an ion mobility enabled Q-TOF mass spectrometer

Comunicaciones a congreso

Field-theoretical renormalization group for a flat two-dimensional Fermi surface

We implement an explicit two-loop calculation of the coupling functions and the self-energy of interacting fermions with a two-dimensional flat Fermi surface in the framework of the field theoretical renormalization group (RG) approach. Throughout the calculation both the Fermi surface and the Fermi velocity are assumed to be fixed and unaffected by interactions. We show that in two dimensions, in a weak coupling regime, there is no significant change in the RG flow compared to the well-known one-loop results available in the literature. However, if we extrapolate the flow to a moderate coupling regime there are interesting new features associated with an anisotropic suppression of the quasiparticle weight Z along the Fermi surface, and the vanishing of the renormalized coupling functions for several choices of the external momenta.Comment: 16 pages and 22 figure

Influència dels desitjos, les necessitats i les xarxes familiars i d'amistat dels estudiants universitaris de la UAB en els seus itineraris formatius en els estudis superiors

L'objectiu del treball és ajudar a la descripció del fenomen del canvi en els itineraris formatius superiors dels estudiants. L'anàlisi es realitza a partir de dades empíriques generades a la UAB durant l'any 2012 i en base als factors contextuals - socio-demogràfics, de perfil i context de l'estudiant - i motivacionals - de vocació acadèmica, vocació laboral, resultats acadèmics, condicions facilitadores, condicions d'empleabilitat, condicions econòmiques, influència de les amistats, estratègies adaptatives o d'oportunitat - que influeixen en les decisions de canvi dels estudiants. En les conclusions es reflexiona sobre les polítiques orientades a mantenir l'equitat en l'accés i en la permanència dels estudiants.El objetivo del trabajo es ayudar a la descripción del fenómeno del cambio en los itinerarios formativos superiores de los estudiantes. El análisis se realiza a partir de datos empíricos generados en la UAB durante el año 2012 y en base a los factores contextuales - socio-demográficos, de perfil y contexto del estudiante - y motivacionales - de vocación académica, vocación laboral, resultados académicos, condiciones facilitadoras, empleabilidad, condiciones económicas, influencia de las amistades, estrategias adaptativas o de oportunidad - que influyen en las decisiones de cambio de los estudiantes. En las conclusiones se reflexiona sobre las políticas orientadas a mantener la equidad en el acceso y en la permanencia de los estudiantes.The aim of this work is to help in the description of the phenomenon of change in itineraries by higher education students. The analysis is performed based on empirical data generated at UAB in 2012 and based on contextual - socio-demographic profile and background of the student - and motivational factors - the academic vocation, labor vocation, academic achievement, enabling conditions, employability, economic conditions, influence of friends, adaptive or opportunity strategies - that influence the decisions of the exchange students. The conclusions reflect on policies designed to maintain equity in access and permanence of students

Ground-based remote sensing of an elevated forest fire aerosol layer at Whistler, BC: implications for interpretation of mountaintop chemistry

On 30 August 2009, intense forest fires in interior British Columbia (BC) coupled with winds from the east and northeast resulted in transport of a broad forest fire plume across southwestern BC. The physico-chemical and optical characteristics of the plume as observed from Saturna Island (AERONET), CORALNet-UBC and the Whistler Mountain air chemistry facility were consistent with forest fire plumes that have been observed elsewhere in continental North America. However, the importance of three-dimensional transport in relation to the interpretation of mountaintop chemistry observations is highlighted on the basis of deployment of both a <i>CL31</i> ceilometer and a single particle mass spectrometer (SPMS) in a mountainous setting. The SPMS is used to identify the biomass plume based on levoglucosan and potassium markers. Data from the SPMS are also used to show that the biomass plume was correlated with nitrate, but not correlated with sulphate or sodium. This study not only provides baseline measurements of biomass burning plume physico-chemical characteristics in western Canada, but also highlights the importance of lidar remote sensing methods in the interpretation of mountaintop chemistry measurements

Friedreich ataxia patient tissues exhibit increased 5-hydroxymethylcytosine modification and decreased CTCF binding at the FXN locus

© 2013 Al-Mahdawi et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use,distribution, and reproduction in any medium, provided the original author and source are credited.This article has been made available through the Brunel Open Access Publishing Fund.Friedreich ataxia (FRDA) is caused by a homozygous GAA repeat expansion mutation within intron 1 of the FXN gene, which induces epigenetic changes and FXN gene silencing. Bisulfite sequencing studies have identified 5-methylcytosine (5 mC) DNA methylation as one of the epigenetic changes that may be involved in this process. However, analysis of samples by bisulfite sequencing is a time-consuming procedure. In addition, it has recently been shown that 5-hydroxymethylcytosine (5 hmC) is also present in mammalian DNA, and bisulfite sequencing cannot distinguish between 5 hmC and 5 mC.The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement number 242193/EFACTS (CS), the Wellcome Trust [089757] (SA) and Ataxia UK (RMP) to MAP

On the determination of the Fermi surface in high-Tc superconductors by angle-resolved photoemission spectroscopy

We study the normal state electronic excitations probed by angle resolved photoemission spectroscopy (ARPES) in Bi2201 and Bi2212. Our main goal is to establish explicit criteria for determining the Fermi surface from ARPES data on strongly interacting systems where sharply defined quasiparticles do not exist and the dispersion is very weak in parts of the Brillouin zone. Additional complications arise from strong matrix element variations within the zone. We present detailed results as a function of incident photon energy, and show simple experimental tests to distinguish between an intensity drop due to matrix element effects and spectral weight loss due to a Fermi crossing. We reiterate the use of polarization selection rules in disentangling the effect of umklapps due to the BiO superlattice in Bi2212. We conclude that, despite all the complications, the Fermi surface can be determined unambiguously: it is a single large hole barrel centered about (pi,pi) in both materials.Comment: Expanded discussion of symmetrization method in Section 5, figures remain the sam

Prevalence of sensorineural hearing loss in children and adolescents with diabetes mellitus

To establish the prevalence of sensorineural hearing loss (SNHL), as well as the predisposing risk factors, in children and adolescents with type 1 diabetes mellitus (T1DM) attending the Service of Endocrino-Pediatrics and Otolaryngology Department of the ‘‘Dr. José Eleuterio González’’ University Hospital and the Materno-Infantil Hospital, from January 2011 to December 2012. Material and methods: A total of 84 children with T1DM, with ages between 6 and 18 years old, were studied. Values of glycated hemoglobin (HbA1c) were assessed and Tonal audiometry and Speech audiometry tests were performed. Results: A total of 84 patients with a diagnosis of T1DM were studied, out of which 12 (14.3%) presented SNHL. Fifty percent of patients with hearing loss were in the age range of 10---13 years old. Regarding time of evolution with the disease (T1DM), 33% of patients with more than 5 years with T1DM presented SNHL, and nearly 88.9% of the patients with less than 5 years with T1DM presented normal hearing (p = 0.011). Moreover, 65.47% of the patients presented complications due to poor glycemic control at some point in the evolution of their disease. All (100%) diabetic patients with SNHL and 91% of the patients without SNHL had HbA1c values greater than 6%. In patients with hearing impairments, 83.3% suffered mild and 16.4% suffered moderate hearing loss. Most presented bilateral hearing loss, with the right ear dominating. Acute frequencies, mainly 8000 kHz, were the most affected

Singular perturbation theory for interacting fermions in two dimensions

We consider a system of interacting fermions in two dimensions beyond the second-order perturbation theory in the interaction. It is shown that the mass-shell singularities in the self-energy, arising already at the second order of the perturbation theory, manifest a non-perturbative effect: an interaction with the zero-sound mode. Resumming the perturbation theory for a weak, short-range interaction and accounting for a finite curvature of the fermion spectrum, we eliminate the singularities and obtain the results for the quasi-particle self-energy and the spectral function to all orders in the interaction with the zero-sound mode. A threshold for emission of zero-sound waves leads a non-monotonic variation of the self-energy with energy (or momentum) near the mass shell. Consequently, the spectral function has a kink-like feature. We also study in detail a non-analytic temperature dependence of the specific heat, $C(T)\propto T^2$. It turns out that although the interaction with the collective mode results in an enhancement of the fermion self-energy, this interaction does not affect the non-analytic term in $C(T)$ due to a subtle cancellation between the contributions from the real and imaginary parts of the self-energy. For a short-range and weak interaction, this implies that the second-order perturbation theory suffices to determine the non-analytic part of $C(T)$. We also obtain a general form of the non-analytic term in $C(T)$, valid for the case of a generic Fermi liquid, \emph{i.e.}, beyond the perturbation theory.Comment: 53 pages, 10 figure