Role of Umklapp Processes in Conductivity of Doped Two-Leg Ladders

Recent conductivity measurements performed on the hole-doped two-leg ladder material $\mathrm{Sr_{14-x}Ca_xCu_{24}O_{41}}$ reveal an approximately linear power law regime in the c-axis DC resistivity as a function of temperature for $x=11$. In this work, we employ a bosonic model to argue that umklapp processes are responsible for this feature and for the high spectral weight in the optical conductivity which occurs beyond the finite frequency Drude-like peak. Including quenched disorder in our model allows us to reproduce experimental conductivity and resistivity curves over a wide range of energies. We also point out the differences between the effect of umklapp processes in a single chain and in the two-leg ladder.Comment: 10 pages, 2 figure

Thermal Conductivity of Spin-1/2 Chains

We study the low-temperature transport properties of clean one-dimensional spin-1/2 chains coupled to phonons. Due to the presence of approximate conservation laws, the heat current decays very slowly giving rise to an exponentially large heat conductivity, $\kappa ~ e^{T^*/T}$. As a result of an interplay of Umklapp scattering and spinon-phonon coupling, the characteristic energy scale $T^*$ turns out to be of order $\Theta_D/2$, where $\Theta_D$ is the Debye energy, rather than the magnetic exchange interaction $J$ -- in agreement with recent measurements in SrCuO compounds. A large magnetic field strongly affects the heat transport by two distinct mechanisms. First, it induces a LINEAR spinon--phonon coupling, which alters the nature of the $T -> 0$ fixed point: the elementary excitations of the system are COMPOSITE SPINON-PHONON objects. Second, the change of the magnetization and the corresponding change of the wave vector of the spinons strongly affects the way in which various Umklapp processes can relax the heat current, leading to a characteristic fractal--like spiky behavior of $\kappa$ when plotted as a function of magnetization at fixed T.Comment: 16 pages, RevTex4, 2 figures included; revised refs. and some useful comments on experimental relevance. On July 12 2005, added an appendix correcting an error in the form of the phonon propagator. The main result is unchange

Transitions between Inherent Structures in Water

The energy landscape approach has been useful to help understand the dynamic properties of supercooled liquids and the connection between these properties and thermodynamics. The analysis in numerical models of the inherent structure (IS) trajectories -- the set of local minima visited by the liquid -- offers the possibility of filtering out the vibrational component of the motion of the system on the potential energy surface and thereby resolving the slow structural component more efficiently. Here we report an analysis of an IS trajectory for a widely-studied water model, focusing on the changes in hydrogen bond connectivity that give rise to many IS separated by relatively small energy barriers. We find that while the system \emph{travels} through these IS, the structure of the bond network continuously modifies, exchanging linear bonds for bifurcated bonds and usually reversing the exchange to return to nearly the same initial configuration. For the 216 molecule system we investigate, the time scale of these transitions is as small as the simulation time scale ($\approx 1$ fs). Hence for water, the transitions between each of these IS is relatively small and eventual relaxation of the system occurs only by many of these transitions. We find that during IS changes, the molecules with the greatest displacements move in small ``clusters'' of 1-10 molecules with displacements of $\approx 0.02-0.2$ nm, not unlike simpler liquids. However, for water these clusters appear to be somewhat more branched than the linear ``string-like'' clusters formed in a supercooled Lennar d-Jones system found by Glotzer and her collaborators.Comment: accepted in PR

In vivo molecular imaging of chemokine receptor CXCR4 expression in patients with advanced multiple myeloma

CXCR4 is a G-protein-coupled receptor that mediates recruitment of blood cells toward its ligand SDF-1. In cancer, high CXCR4 expression is frequently associated with tumor dissemination and poor prognosis. We evaluated the novel CXCR4 probe [(68)Ga]Pentixafor for in vivo mapping of CXCR4 expression density in mice xenografted with human CXCR4-positive MM cell lines and patients with advanced MM by means of positron emission tomography (PET). [(68)Ga]Pentixafor PET provided images with excellent specificity and contrast. In 10 of 14 patients with advanced MM [(68)Ga]Pentixafor PET/CT scans revealed MM manifestations, whereas only nine of 14 standard [(18)F]fluorodeoxyglucose PET/CT scans were rated visually positive. Assessment of blood counts and standard CD34(+) flow cytometry did not reveal significant blood count changes associated with tracer application. Based on these highly encouraging data on clinical PET imaging of CXCR4 expression in a cohort of MM patients, we conclude that [(68)Ga]Pentixafor PET opens a broad field for clinical investigations on CXCR4 expression and for CXCR4-directed therapeutic approaches in MM and other diseases

Géodynamique andine : résumés étendus = Andean geodynamics : extended abstracts

Nous présentons ici les résultats d'investigations gravimétriques et sismiques dans les Andes Centrales du sud (20°-28° S) effectuées durant les années 80 et le début des années 90. Les structures grossières de la croûte peuvent être déterminées de manière à couvrir les unités morphostructurales principales des Andes entre 21° et 25° sud. Les investigations gravimétriques et sismiques ont été centrées sur les structures de l'arc et de l'avant-arc afin de fournir une connaissance plus détaillée de la structure de la croûte dans cette région. (Résumé d'auteur

Géodynamique andine : résumés étendus = Andean geodynamics : extended abstracts

De 1993 à 1995, le groupe international MIGRA constitué de participants du Chili, d'Argentine et d'Allemagne ont relevé environ 2000 nouvelles mesures gravimétriques le long d'un géotraverse des Andes couvrant le nord du Chili et le nord-ouest de l'Argentine entre 64°-71° ouest et 20°-29° sud. La base de données comprenant les coordonnées des stations, des grilles de données de 10x10 km de l'anomalie à l'air libre, de différents types d'anomalies de Bouguer ainsi que l'anomalie isostatique résiduelle sont ici représentés dans une carte du champ isostatique résiduel, avec une interprétation sommaire. (Résumé d'auteur

Knochenmarktransplantation bei akuter Leukämie: Prophylaktische Antiserumbehandlung des Knochenmarks zur Unterdrückung einer Transplantat-gegen-Wirt-Reaktion.

Anti-human-thymocyte globulin (AHTZG) was applied to prevent GvHD in clinical bone marrow transplantation. AHTZG produced by absorption with several cell preparations reacted specifically with T-lymphocyte populations and was no longer inhibitory to human CFUc and bone marrow growth in diffusion chambers. Marrow grafts of 14 patients with ALL were incubated in vitro with AHTZG and transferred to the recipients conditioned with antileukemic chemotherapy and total body irradiation of 1000 rad. Ten patients were transplanted after relaps, four patients during remission. The patients tolerated the marrow without side effects and a hemopoietic engraftment was seen in 12 cases. Three patients showed signs of GvHD on the skin, two of them showed later on also manifestations in the liver. In the other cases no GvHD could be detected. Five out of 14 patients are still alive between 144 and 964 days post transplantation in remission