Aharonov-Bohm oscillations in the local density of states

The scattering of electrons with inhomogeneities produces modulations in the local density of states of a metal. We show that electron interference contributions to these modulations are affected by the magnetic field via the Aharonov-Bohm effect. This can be exploited in a simple STM setup that serves as an Aharonov-Bohm interferometer at the nanometer scale.Comment: 4 pages, 2 figures. v2 added reference

Interplay of magnetic and structural transitions in Fe-based pnictide superconductors

The interplay between the structural and magnetic phase transitions occurring in the Fe-based pnictide superconductors is studied within a Ginzburg-Landau approach. We show that the magnetoelastic coupling between the corresponding order parameters is behind the salient features observed in the phase diagram of these systems. This naturally explains the coincidence of transition temperatures observed in some cases as well as the character (first or second-order) of the transitions. We also show that magnetoelastic coupling is the key ingredient determining the collinearity of the magnetic ordering, and we propose an experimental criterion to distinguish between a pure elastic from a spin-nematic-driven structural transition.Comment: 5 pages, 3 figures. v2: Fig. 1 improved, references added

Magnetoelastic Effects in Iron Telluride

Iron telluride doped lightly with selenium is known to undergo a first order magneto-structural transition before turning superconducting at higher doping. We study the effects of magneto-elastic couplings on this transition using symmetry considerations. We find that the magnetic order parameters are coupled to the uniform monoclinic strain of the unit cell with one iron per cell, as well as to the phonons at high symmetry points of the Brillouin zone. In the magnetic phase the former gives rise to monoclinic distortion while the latter induces dimerization of the ferromagnetic iron chains due to alternate lengthening and shortening of the nearest-neighbour iron-iron bonds. We compare this system with the iron arsenides and propose a microscopic magneto-elastic Hamiltonian which is relevant for all the iron based superconductors. We argue that this describes electron-lattice coupling in a system where electron-electron interaction is crucial.Comment: 5 pages, 2 figure

La epopeya, de los Lumière a la HBO : aspectos dialécticos de un estado de la cuestión

Bajo el peso abrumador del cine neomitologista (1957-c. 1970), y algún fracaso de público, los estudiosos guardaron el recuerdo del cine de romanos en un basto féretro con la etiqueta peplum, un disfemismo afrancesado. Pasó casi desapercibido que, ya en 1968, la TV había tomado el relevo en forma de una Odisea de Franco Rossi, autor también de una posterior Eneida. Poco más de un lustro después, la serie Yo, Claudio revolucionó el género en un relato casi desprovisto de los munera que atraían el público a las salas. Salvo casos singulares, las series fueron luego la expresión mediática del mundo clásico, hasta que en los años 2000 Gladiator retomó la epopeya para la pantalla grande, sin que la TV, con Roma de HBO en el mascarón de proa, perdiera aliento en absoluto. En este trabajo se pretende proponer una visión de conjunto que respete el continuum natural entre cine y TV: la evolución de temas, tópicos y mitos de ese virtual mundo clásico, que fue real un día en latín y griego

Ressenyes

Index de les obres ressenyades: Harm PINKSTER, Sintaxis y semántica del latí

Membranes polimèriques enzimàtiques : aplicació al tractament de biomassa vegetal per a la recuperació d'oligosacàrids /

Consultable des del TDXTítol obtingut de la portada digitalitzadaActualment, els processos orientats a la reducció de residus i l'obtenció de productes d'alt valor afegit es presenten com una fita amb perspectives prometedores. En aquesta tesi es dissenyen membranes polimèriques selectives per al tractament de materials lignocel·lulòsics. L'enzim endo-1,4-?-xilanasa II, que hidrolitza enllaços 1,4-?-glicosídics a l'esquelet del xilà, s'immobilitza a membranes per enllaç covalent, per a recuperar oligosacàrids de la hidròlisi d'aquest polímer. L'interès d'immobilitzar enzims en suports polimèrics rau en la reducció del cost i la simplificació del procés global, a conseqüència de la possibilitat de reutilizar l'enzim immobilitzat mentre conservi la seva activitat catalítica. S'investiguen dos tipus de membranes polimèriques i mètodes de immobilització per enllaç covalent entre grups funcionals de l'enzim i del suport. Les primeres són membranes d'acrilat de polisulfona (ACPS). La immobilització de la proteïna es confirma per anàlisi de aminoàcids per HPLC i comparació amb l'anàlisi de la proteïna en dissolució. Les altres membranes (N25) estan constituïdes per polímers monolítics. Les propietats físiques i químiques d'aquests materials depenen de la selecció i de la quantitat dels components de la dissolució precursora de membrana. S'optimitza aquesta composició de la dissolució precursora per a obtenir la màxima activitat enzimàtica. Es comparen diferents procediments d'immobilització per ambdues membranes per a avaluar la capacitat d'immobilització. Les membranes ACPS retenen més enzim que les N25, tot i que no comporta major activitat enzimàtica, ja que aquesta depèn de l'estabilització de la proteïna immobilitzada en cada cas. Es proposa l'ús de tècniques de biologia molecular per a dur a terme la immobilització dirigida, i evitar el bloqueig del centre actiu de les molècules d'enzim per unió directa amb el suport per aquest punt. La influència de la immobilització en paràmetres d'activitat enzimàtica (pH i temperatura) s'estudia i es compara amb els paràmetres òptims de l'enzim lliure. Els valors de la constant de Michaelis-Menten no difereixen significativament entre l'enzim lliure i immobilitzat, de manera que l'afinitat del catalitzador respecte dels substrats considerats roman inalterada un cop immobilitzat. Per a la caracterització física de las membranes, s'utilitzen diferents tècniques, com la microscòpia electrònica d'escombrat (SEM), a partir de la qual s'observen diferències de simetria i porositat entre els dos tipus de membranes. Per microscòpia de força atòmica (AFM) no es detecten diferències en un mateix tipus de membranes segons continguin o no enzim immobilitzat. De la determinació de fluxos d'aigua pura, els valors més alts s'obtenen amb les membranes N25. A partir de mesures d'adsorció-desorció de gasos s'observa que les membranes N25 tenen major àrea superficial i distribucions de porus amb major diàmetre mitjà. Les mesures d'angle de contacte evidencien un major caràcter hidrofílic de les membranes N25 que les ACPS, que augmenta en incrementar la quantitat d'enzim immobilitzat. Les membranes s'apliquen al tractament de biomassa, emprant dos mòduls de membrana diferents. Solament s'obté separació dels productes del substrat inicial quan s'utilitza el mòdul de filtració frontal aplicant pressió. La major concentració de productes d'hidròlisi s'obté amb les membranes N25 en el tractament de Birchwood xylan, malgrat que no és possible reutilitzar-les en una segona hidròlisi consecutiva amb nova dissolució de substrat. En canvi, en tractar substrats procedents de closca de moresc, les membranes ACPS es poden reutilitzar, malgrat que la concentració de productes és inferior que en la primera hidròlisi. Els productes obtinguts s'analitzen per un mètode colorimètric, per electroforesi capil·lar, per cromatografia per permeació en gel, i per ionització per làser assistida per matriu amb analitzador de temps de vol (MALDI-TOF-MS). L'última permet determinar el grau de polimerització dels productes, obtenint com a majoritari xilotriosa. Finalment s'avalua el procés global i es presenten propostes de millora.Nowadays, processes oriented to waste reduction and recovery of high added value products are a promising target. In this thesis, enzymatic polymeric membranes are designed for the treatment of vegetal biomass waste like lignocellulosic materials. The enzyme endo-1,4-?-xylanase II, which hydrolyzes 1,4-?-glycosidic linkages of the xylan backbone, is immobilized in the membranes through a covalent bond in order to recover oligosaccharides by xylan hydrolysis. The interest for the attachment of enzymes on polymeric supports relies on the reduction in the cost and the simplification of the process, comparing to processes with enzymes in solution, due to the ability for reusing the enzyme for as long as its catalytic activity is maintained. Two different polymeric membranes and covalent immobilization methods (between functional groups of the enzymes and groups in the support) are investigated. The first consist on polysulfone acrylate (ACPS). Protein immobilization is confirmed by HPLC by comparing the amino acid content in ACPS membranes with the amino acid content in the free xylanase solution. The other membranes (N25) are based in monolithic polymers. Their physical and chemical characteristics can be finely tuned by selecting the appropriate constituents and their content in the precursor solution. The composition of different membranes, regarding the amount of three components in the membrane precursor solution is optimized to obtain the highest catalytic activity. Different enzyme immobilization conditions in both membranes are compared to evaluate their immobilization capacity. ACPS membranes retained more enzyme than N25, although this does not imply higher enzymatic activity, since it depends on the stabilization of the immobilized protein. The use of molecular biology techniques is proposed to avoid the catalytic site blocking, by performing site directed immobilization. The influence of the immobilization in enzymatic activity parameters (temperature and pH) is studied for both membranes and compared with data for the free enzyme. Regarding the enzyme kinetic parameters, KM values for free and immobilized enzyme in the two membranes are close, meaning that the enzyme affinity for the substrates considered remains intact. The immobilization time is optimized and the enzymatic activity stability of the immobilized enzymes is studied. Different techniques are used for the physical characterization of membranes. Scanning Electron Microscopy (SEM) showed differences in symmetry and pore structure between membrane types. No significant differences are observed when comparing Atomic Force Microscopy (AFM) images of membranes without/with enzyme. Pure water fluxes are determined and N25 membranes exhibit higher fluxes than ACPS. From gas adsorption-desorption is observed that N25 membranes have higher surface area and pore distributions with higher average pore diameter than ACPS. Contact angle measurements show higher hydrophilic character for N25 than ACPS, and hydrophilicity increases with immobilized enzyme in both membranes. The enzymatic membranes are used in biomass treatment with two membrane modules. Separation of the products from the initial substrate is achieved only with the dead-end module. By using N25 membranes higher yields of hydrolysis products (expressed as xylose) from enzymatic hydrolysis of Birchwood xylan (0.650 µmol/ml) are obtained, compared to ACPS (0.150 µmol/m). It is not possible to reuse N25 membranes in a consecutive hydrolysis with new substrate. In contrast, when treating samples proceeding from the direct treatment of corn shells, ACPS membranes can be reused, although the product concentration is lower than during the first hydrolysis. The hydrolysis products are analyzed by a colorimetric assay, Capillary Electrophoresis (CE), Gel Permeation Chromatography (GPC) and the degree of polymerization is determined by Matrix Assisted Laser Desorption Ionization Time Of Flight Mass Spectrometry (MALDI-TOF-MS). Almost in all samples the unique observed specie is xylotriose. Finally, a global evaluation and improvements to be considered during future research are presented

Laparoscopic image analysis for automatic tracking of surgical tools

Laparoscopy is a surgical technique nowadays embedded in the clinical routine. Recent researches have been focused on analysing video information captured by the endoscope for extracting cues useful for surgeons, such as depth information. In particular, the 3D pose estimation of the surgical tools presents three important added values: (1) to extract objective parameters for the surgical training stage, (2) to develop an image-guided surgery based on the knowledge of the surgery tools localization, (3) to design new roboticsystems for an automatic laparoscope positioning, according to the visual feedback. Tool’s shape and orientation in the image is the key to get its 3D position. This work presents an image analysis for automatic laparoscopic tool’s detection along the recorded video without extra tool markers, using an edges detection strategy. Also, this analysis includes a previous stage of barrel distortion correction for videoendoscopic image

Building Blocks of Topological Quantum Chemistry: Elementary Band Representations

The link between chemical orbitals described by local degrees of freedom and band theory, which is defined in momentum space, was proposed by Zak several decades ago for spinless systems with and without time-reversal in his theory of "elementary" band representations. In Nature 547, 298-305 (2017), we introduced the generalization of this theory to the experimentally relevant situation of spin-orbit coupled systems with time-reversal symmetry and proved that all bands that do not transform as band representations are topological. Here, we give the full details of this construction. We prove that elementary band representations are either connected as bands in the Brillouin zone and are described by localized Wannier orbitals respecting the symmetries of the lattice (including time-reversal when applicable), or, if disconnected, describe topological insulators. We then show how to generate a band representation from a particular Wyckoff position and determine which Wyckoff positions generate elementary band representations for all space groups. This theory applies to spinful and spinless systems, in all dimensions, with and without time reversal. We introduce a homotopic notion of equivalence and show that it results in a finer classification of topological phases than approaches based only on the symmetry of wavefunctions at special points in the Brillouin zone. Utilizing a mapping of the band connectivity into a graph theory problem, which we introduced in Nature 547, 298-305 (2017), we show in companion papers which Wyckoff positions can generate disconnected elementary band representations, furnishing a natural avenue for a systematic materials search.Comment: 15+9 pages, 4 figures; v2: minor corrections; v3: updated references (published version

Band Connectivity for Topological Quantum Chemistry: Band Structures As A Graph Theory Problem

The conventional theory of solids is well suited to describing band structures locally near isolated points in momentum space, but struggles to capture the full, global picture necessary for understanding topological phenomena. In part of a recent paper [B. Bradlyn et al., Nature 547, 298 (2017)], we have introduced the way to overcome this difficulty by formulating the problem of sewing together many disconnected local "k-dot-p" band structures across the Brillouin zone in terms of graph theory. In the current manuscript we give the details of our full theoretical construction. We show that crystal symmetries strongly constrain the allowed connectivities of energy bands, and we employ graph-theoretic techniques such as graph connectivity to enumerate all the solutions to these constraints. The tools of graph theory allow us to identify disconnected groups of bands in these solutions, and so identify topologically distinct insulating phases.Comment: 19 pages. Companion paper to arXiv:1703.02050 and arXiv:1706.08529 v2: Accepted version, minor typos corrected and references added. Now 19+epsilon page

Inteligencia interpersonal : conceptos clave

El propósito de este trabajo es el de delimitar el espacio conceptual de la inteligencia interpersonal, relacionándolo con las situaciones en las cuales se utiliza. Para ello se establecen, en primer lugar, los aspectos relacionados con la naturaleza intelectual y el tipo de objetos representados. Sigue un apartado dedicado a los orígenes de la misma y su función en la adaptación de la especie humana. Un tercer apartado trata del tipo de procedimientos adecuados para su medición, no como una recopilación de instrumentos comúnmente utilizados, sino como una manera de hacer explícitos qué tipo de indicios son buena prueba de este tipo de inteligencia. A continuación se describen algunas de las principales confusiones asociadas a la idea de esta forma de inteligencia, integrando finalmente todos los aspectos tratados en el apartado de conclusionesThe purpose of this paper is to delimit the conceptual space of interpersonal intelligence, relating it to situations in which it is used. To this end, we first identify some aspects of an intellectual nature and the type of objects represented. The next section is devoted to the origins of interpersonal intelligence and its role in human adaptation. A third section focuses on the type of procedures for its measurement, not as a collection of tools commonly used, but as a way to make explicit the kind of evidence that is appropriate as good indicators of this intelligence. Finally, we describe some of the main confusions associated with the idea of this form of intelligence, integrating all aspects previously discusse