Wick's Theorem and a New Perturbation Theory Around the Atomic Limit of Strongly Correlated Electron Systems

A new type of perturbation expansion in the mixing $V$ of localized orbitals with a conduction-electron band in the $U\to\infty$ Anderson model is presented. It is built on Feynman diagrams obeying standard rules. The local correlations of the unperturbed system (the atomic limit) are included exactly, no auxiliary particles are introduced. As a test, an infinite-order ladder-type resummation is analytically treated in the Kondo regime, recovering the correct energy scale. An extension to the Anderson-lattice model is obtained via an effective-site approximation through a cumulant expansion in $V$ on the lattice. Relation to treatments in infinite spatial dimensions are indicated.Comment: selfextracting postscript file containing entire paper (10 pages) including 3 figures, in case of trouble contact author for LaTeX-source or hard copies (prep0994

Orthopädische Biomechanik

Das Buch beschreibt Gedankengänge und Vorgehensweisen der orthopädischen Biomechanik, den Kenntnisstand zu Belastung und Beanspruchung des Haltungs- und Bewegungsapparates sowie die Reaktion der Gewebe auf mechanische Einflüsse exakt, aber mit einem Minimum an mathematischer und physikalischer Argumentation. Es gliedert sich in die Abschnitte I Grundlagen aus der Mechanik II Grundlagen aus der Mathematik III Mechanische Aspekte des Haltungs- und Bewegungsapparates IV Übungsaufgaben mit ausgearbeiteten Lösungen Zahlreiche Abbildungen unterstützen die anschauliche Darstellung. Ein Buch für Orthopäden, Ingenieure, Naturwissenschaftler, Physiotherapeuten und Orthopädietechniker in den Bereichen Forschung und Entwicklung von Orthopädie und Rehabilitation.  <br/

Neel order, quantum spin liquids and quantum criticality in two dimensions

This paper is concerned with the possibility of a direct second order transition out of a collinear Neel phase to a paramagnetic spin liquid in two dimensional quantum antiferromagnets. Contrary to conventional wisdom, we show that such second order quantum transitions can potentially occur to certain spin liquid states popular in theories of the cuprates. We provide a theory of this transition and study its universal properties in an $\epsilon$ expansion. The existence of such a transition has a number of interesting implications for spin liquid based approaches to the underdoped cuprates. In particular it considerably clarifies existing ideas for incorporating antiferromagnetic long range order into such a spin liquid based approach.Comment: 18 pages, 17 figure

Investigation of soluble adhesion molecules in cancer: beneficial approach or expensive toy? The case of intercellular adhesion molecule-1 (sICAM-1)

Adhesion molecules are key topobiological components in almost any kind of cell-cell and cell-matrix interaction in both human physiology and pathology. Heterogeneous processes as platelet adhesion to subendothelial matrix components or leukocyte extravasation at sites of tissue damage are at least in part mediated by adhesion molecules and their corresponding receptors (counter receptors). Using a multitude of modem analytical and preparative approaches ranging from "simple" immunohistochemistry to cloning and gene transfer, in vitro studies provided detailed data on a variety of adhesion molecules and their receptors. However, compared to the speedy accumulation of basic knowledge the evaluation of the diagnostic usefulness of adhesion molecules is still in its infancy.Biomedical Reviews 1994; 3: 73-75

X-ray morphology of cluster-mass haloes in self-interacting dark matter

We perform cosmological zoom-in simulations of $19$ relaxed cluster-mass haloes with the inclusion of adiabatic gas in the cold dark matter (CDM) and self-interacting dark matter (SIDM) models. These clusters are selected as dynamically relaxed clusters from a parent simulation with $M_{\rm 200} \simeq 1\operatorname{-}3\times 10^{15}\,{\rm M}_{\odot}$. Both the dark matter and the intracluster gas distributions in SIDM appear more spherical than their CDM counterparts. Mock X-ray images are generated based on the simulations and are compared to the real X-ray images of $84$ relaxed clusters selected from the Chandra and ROSAT archives. We perform ellipse fitting for the isophotes of mock and real X-ray images and obtain the ellipticities at cluster-centric radii of $r\simeq 0.1\operatorname{-}0.2\,R_{\rm 200}$. The X-ray isophotes in SIDM models with increasing cross-sections are rounder than their CDM counterparts, which manifests as a systematic shift in the distribution function of ellipticities. Unexpectedly, the X-ray morphology of the observed non-cool-core clusters agrees better with SIDM models with cross-section $(\sigma/m)= 0.5\operatorname{-}1~{\rm cm}^2/{\rm g}$ than CDM and SIDM with $(\sigma/m)=0.1\,{\rm cm}^2/{\rm g}$. Our statistical analysis indicates that the latter two models are disfavored at the $68\%$ confidence level (as conservative estimates). This conclusion is not altered by shifting the radial range of measurements or applying temperature selection criterion. However, the primary uncertainty originates from the lack of baryonic physics in the adiabatic model, such as cooling, star formation and feedback effects, which still have the potential to reconcile CDM simulations with observations.Comment: Accepted by MNRA

Where is the pi particle?

We discuss the interplay of particle-particle and particle-hole spin-triplet channels in high-T_c superconductors using a quasiparticle dispersion motivated by angle-resolved photoemission. Within a generalized RPA, we find a well defined antibound state of two holes, the pi resonance of Demler and Zhang, as well as a bound state of a particle and a hole, the spin exciton. We show that the energy of the pi resonance always exceeds 2 Delta, twice the maximum d-wave gap, therefore the neutron resonance observed in the cuprates around energy Delta is most likely a spin exciton. At the same time, we speculate that the pi particle can exist at higher energies and might be observed in neutron scattering around 100 meV.Comment: RevTeX, 5 pages, 4 eps figure

Interlayer pair tunneling and gap anisotropy in YBa2_2Cu3_3O7−δ_{7-\delta}

Recent ARPES measurement observed a large $ab$-axis gap anisotropy, $\Delta(0,\pi)/\Delta(\pi,0)=1.5$, in clean YBa$_2$Cu$_3$O$_{7-\delta}$. This indicates that some sub-dominant component may exist in the $d_{x^2-y^2}$-wave dominant gap. We propose that the interlayer pairing tunneling contribution can be determined through the investigation of the order parameter anisotropy. Their potentially observable features in transport and spin dynamics are also studied.Comment: 4 pages, 3 figure

In situ nanoindentation during electrochemical hydrogen charging: a comparison between front-side and a novel back-side charging approach

The effects of hydrogen in metals are a pressing issue causing severe economic losses due to material deterioration by hydrogen embrittlement. A crucial understanding of the interactions of hydrogen with different microstructure features can be reached by nanoindentation due to the small volumes probed. Even more, in situ testing while charging the sample with hydrogen prevents the formation of concentration gradients due to hydrogen desorption. Two custom electrochemical cells for in situ testing were built in-house to charge the sample with hydrogen during nanoindentation: “front-side” charging with the sample and the indenter tip immersed into the electrolyte, and “back-side” charging where the analyzed region is never in contact with the solution. During front-side charging, surface degradation often occurs which also negatively influences analyses after hydrogen charging. The back-side charging approach proposed in this work is a promising technique for studying in situ the effects of hydrogen in alloys under mechanical loads, while completely excluding the influence of the electrolyte on the nanoindented surface. Hydrogen diffusion from the charged back-side toward the testing surface is here demonstrated by Kelvin probe measurements in ferritic FeCr alloys, used as a case study due to the high mobility of hydrogen in the bcc lattice. During nanoindentation, a reduction on the shear stress necessary for dislocations nucleation due to hydrogen was observed using both setups; however, the quantitative data differs and a contradictory behavior was found in hardness measurements. Finally, some guidelines for the use of both approaches and a summary of their advantages and disadvantages are presented

El estudio de los riesgos con origen hidrológico en el su-reste de la Península Ibérica. Enfoque geográfico y plani-ficación territorial

This paper shows the current studies on hydrological risks in the outh-east Spain, a region specially producing hazard situations. This area is one of the most arid regions of Europe, characterized by extraordinary rains of high hourly intensity causing bulky discharges and overflows, but also by the installation of dense urban nucleus in coastal areas and fertile plains. The scanty one, or in occasions unfortunate, dialog between environment and man has done of this one an area of notable interest for numerous researchers on the risk processes associated with hydrological extreme events. The ephemeral flow regime and the hydraulic effects of the linear infrastructures and drainage works complicate the estimation of the flood discharges, increasing the above mentioned degree of complexity. There are several models, programs and projects focused on these questions, but a major knowledge is still absent on this type of risk processes, particularly in relation with the generation of flood areas. For it is necessary a cartographic information base of more detail and the incorporation of factors till now very little considered as those hydro-morphological or the indicators of vulnerability.El presente artículo muestra el estado de la cuestión en el análisis de los riesgos hidrológicos de una región natural española especialmente productora de situaciones de peligro: el Sureste de la Península Ibérica. Los graves impactos que este tipo de peligros naturales tienen en la economía, la sociedad y el medio ambiente de esta región hacen que el enfoque geográfico revista aquí especial importancia en el estudio de sus riesgos derivados, particularmente en relación con la evaluación y gestión de los mismos, y su indudable implicación en las políticas de planificación territorial. Ésta es una de las regiones más áridas de Europa, caracterizada por lluvias extraordinarias de alta intensidad horaria capaces provocar abultados caudales y desbordamientos de cauces, pero también por la instalación de núcleos densos de poblamiento en sus áreas litorales y de vega. El escaso, o en ocasiones desafortunado, diálogo entre me-dio natural y hombre ha hecho de ésta una zona de notable interés para gran número de investigadores en temas de riesgos asociados a fenómenos hidrológicos extremos. El carácter efímero de las corrientes y los efectos hidráulicos de las infraestructuras lineales y obras de drenaje complican la estimación de los cau-dales de avenida, aumentando dicho grado de complejidad. Aun cuando existen ya varios modelos, pro-gramas y proyectos enfocados a estas cuestiones todavía falta un mayor conocimiento sobre este tipo de procesos de riesgo, particularmente en relación con la generación de áreas inundables, para la que se ne-cesita una información cartográfica base de mayor detalle y la incorporación de factores hasta ahora muy poco considerados como los hidromorfológicos o los indicadores de vulnerabilidad

Spin correlations in the algebraic spin liquid - implications for high Tc superconductors

We propose that underdoped high $T_c$ superconductors are described by an algebraic spin liquid (ASL) at high energies, which undergoes a spin-charge recombination transition at low energies. The spin correlation in the ASL is calculated via its effective theory - a system of massless Dirac fermions coupled to a U(1) gauge field. We find that without fine tuning any parameters the gauge interaction strongly enhances the staggered spin correlation even in the presence of a large single particle pseudo-gap. This allows us to show that the ASL plus spin-charge recombination picture can explain many highly unusual properties of underdoped high $T_c$ superconductors.Comment: 22 pages, 18 figures, submitted to PR