On Coordinate Transformations in Planar Noncommutative Theories

We consider planar noncommutative theories such that the coordinates verify a space-dependent commutation relation. We show that, in some special cases, new coordinates may be introduced that have a constant commutator, and as a consequence the construction of Field Theory models may be carried out by an application of the standard Moyal approach in terms of the new coordinates. We apply these ideas to the concrete example of a noncommutative plane with a curved interface. We also show how to extend this method to more general situations.Comment: 20 pages, 1 figure. references adde

Suppression of ferromagnetism in CeSi_1.81 under temperature and pressure

We have studied the pressure dependence of the magnetization of single crystalline CeSi_1.81. At ambient pressure ferromagnetism develops below T_C = 9.5 Below ~ 5 K an additional shoulder in low-field hysteresis loops and a metamagnetic crossover around 4 T suggest the appearance of an additional magnetic modulation to the ferromagnetic state. The suppression of the magnetic order in CeSi_1.81 as function of temperature at ambient pressure and as function of pressure at low temperature are in remarkable qualitative agreement. The continuous suppression of the ordered moment at p ~ 13.1 kbar suggests the existence of a ferromagnetic quantum critical point in this material.Comment: 9 pages, 9 figures, to be published in Physical Review

New insight into the physics of iron pnictides from optical and penetration depth data

We report theoretical values for the unscreened plasma frequencies Omega_p of several Fe pnictides obtained from DFT based calculations within the LDA and compare them with experimental plasma frequencies obtained from reflectivity data. The sizable renormalization observed for all considered compounds points to the presence of many-body effects beyond the LDA. From the large empirical background dielectric constant of about 12-15, we estimate a large arsenic polarizability of about 9.5 +- 1.2 Angstroem^3 where the details depend on the polarizabilities of the remaining ions taken from the literature. This large polarizability can significantly reduce the value of the Coulomb repulsion U_d about 4 eV on iron known from iron oxides to a level of 2 eV or below. In general, this result points to rather strong polaronic effects as suggested by G.A. Sawatzky et al., in Refs. arXiv:0808.1390 and arXiv:0811.0214 (Berciu et al.). Possible consequences for the conditions of a formation of bipolarons are discussed, too. From the extrapolated muon spin rotation penetration depth data at T= 0 and the experimental Omega_p we estimate the total coupling constant lambda_tot for the el-boson interaction within the Eliashberg-theory adopting a single band approximation. For LaFeAsO_0.9F_0.1 a weak to intermediately strong coupling regime and a quasi-clean limit behaviour are found. For a pronounced multiband case we obtain a constraint for various intraband coupling constants which in principle allows for a sizable strong coupling in bands with either slow electrons or holes.Comment: 34 pages, 10 figures, submitted to New Journal of Physics (30.01.2009

Optical Study of LaO_0.9F_0.1FeAs: Evidence for a Weakly Coupled Superconducting State

We have studied the reflectance of the recently discovered superconductor LaO_0.9F0.FeAs in a wide energy range from the far infrared to the visible regime. We report on the observation of infrared active phonons, the plasma edge (PE) and possible interband transitions. On the basis of this data and the reported in-plane penetration depth lambda_L(0) about 254 nm [H. Luetkens et al., Phys. Rev. Lett. v. 101, 0970009 (2008)] a disorder sensitive relatively small value of the total electron electron-boson coupling constant lambda_tot=lambda_e-ph+lambda_e-sp ~ 0.6 +- 0.35 can be estimated adopting an effective single-band picture.Comment: Changed title, updated references, final published versio

Ce-L3-XAS study of the temperature dependence of the 4f occupancy in the Kondo system Ce2Rh3Al9

We have used temperature dependent x-ray absorption at the Ce-L3 edge to investigate the recently discovered Kondo compound Ce2Rh3Al9. The systematic changes of the spectral lineshape with decreasing temperature are analyzed and found to be related to a change in the $4f$ occupation number, n_f, as the system undergoes a transition into a Kondo state. The temperature dependence of $n_f$ indicates a characteristic temperature of 150K, which is clearly related with the high temperature anomaly observed in the magnetic susceptibility of the same system. The further anomaly observed in the resistivity of this system at low temperature (ca. 20K) has no effect on n_f and is thus not of Kondo origin.Comment: 7 pages, three figures, submitted to PR

A Homogenous Set of Globular Cluster Relative Distances and Reddenings

We present distance modulus and reddening determinations for 72 Galactic globular clusters from the homogeneous photometric database of Piotto et al. (2002), calibrated to the HST flight F439W and F555W bands. The distances have been determined by comparison with theoretical absolute magnitudes of the ZAHB. For low and intermediate metallicity clusters, we have estimated the apparent Zero Age Horizontal Branch (ZAHB) magnitude from the RR Lyrae level. For metal rich clusters, the ZAHB magnitude was obtained from the fainter envelope of the red HB. Reddenings have been estimated by comparison of the HST colour-magnitude diagrams (CMD) with ground CMDs of low reddening template clusters. The homogeneity of both the photometric data and the adopted methodological approach allowed us to obtain highly accurate relative cluster distances and reddenings. Our results are also compared with recent compilations in the literature.Comment: 12 pages, 6 figures, accepted for publication in Astronomy & Astrophysic

Sildenafil added to pirfenidone in patients with advanced idiopathic pulmonary fibrosis and risk of pulmonary hypertension: A Phase IIb, randomised, double-blind, placebo-controlled study – Rationale and study design

Background: Pulmonary hypertension (PH) is commonly observed in patients with advanced idiopathic pulmonary fibrosis (IPF). Despite the availability of therapies for both IPF and PH, none are approved for PH treatment in the context of significant pulmonary disease. This study will investigate the use of sildenafil added to pirfenidone in patients with advanced IPF and risk of PH, who represent a group with a high unmet medical need. Methods: This Phase IIb, randomised, double-blind, placebo-controlled trial is actively enrolling patients and will study the efficacy, safety and tolerability of sildenafil or placebo in patients with advanced IPF and intermediate or high probability of Group 3 PH who are receiving a stable dose of pirfenidone. Patients with advanced IPF (diffusing capacity for carbon monoxide 6440% predicted) and risk of Group 3 PH (defined as mean pulmonary arterial pressure 6520 mm Hg with pulmonary arterial wedge pressure 6415 mm Hg on a previous right-heart catheterisation [RHC], or intermediate/high probability of Group 3 PH as defined by the 2015 European Society of Cardiology/European Respiratory Society guidelines) are eligible. In the absence of a previous RHC, patients with an echocardiogram showing a peak tricuspid valve regurgitation velocity 652.9 m/s can enrol if all other criteria are met. The primary efficacy endpoint is the proportion of patients with disease progression over a 52-week treatment period. Safety will be evaluated descriptively. Discussion: Combination treatment with sildenafil and pirfenidone may warrant investigation of the treatment of patients with advanced IPF and pulmonary vascular involvement leading to PH