Temperature-Dependent X-Ray Absorption Spectroscopy of Colossal Magnetoresistive Perovskites

The temperature dependence of the O K-edge pre-edge structure in the x-ray absorption spectra of the perovskites La(1-x)A(x)MnO(3), (A = Ca, Sr; x = 0.3, 0.4) reveals a correlation between the disappearance of the splitting in the pre-edge region and the presence of Jahn-Teller distortions. The different magnitudes of the distortions for different compounds is proposed to explain some dissimilarity in the line shape of the spectra taken above the Curie temperature.Comment: To appear in Phys. Rev. B, 5 pages, 3 figure

Detection of noise-corrupted sinusoidal signals with Josephson junctions

We investigate the possibility of exploiting the speed and low noise features of Josephson junctions for detecting sinusoidal signals masked by Gaussian noise. We show that the escape time from the static locked state of a Josephson junction is very sensitive to a small periodic signal embedded in the noise, and therefore the analysis of the escape times can be employed to reveal the presence of the sinusoidal component. We propose and characterize two detection strategies: in the first the initial phase is supposedly unknown (incoherent strategy), while in the second the signal phase remains unknown but is fixed (coherent strategy). Our proposals are both suboptimal, with the linear filter being the optimal detection strategy, but they present some remarkable features, such as resonant activation, that make detection through Josephson junctions appealing in some special cases.Comment: 22 pages, 13 figure

Periplasm Organization in \u3ci\u3eTreponema denticola\u3c/i\u3e as Studied by Cryo-electron Tomography

As a spirochete, the genus Treponema is one of the few major bacterial groups whose natural phylogenic relationships are evident at the level of gross phenotypic characteristics such as their morphology. Treponema spp. are highly invasive due to their unique motility in dense media, and their ability to penetrate cell layers [1]. This feature is associated with the helical cell body and the presence of flagellar filaments in the periplasm [2]. Treponema denticola is an oral pathogen involved in endodontic infections and periodontal diseases. The presence and quantity of T. denticola in the subgingival biofilm is correlated with the severity of periodontal disease and tissue destruction [3,4]. The organism has also been detected in 75% of severe endodontic abscesses [5]. A better understanding of Treponema ultrastructure and motility will aid development of new strategies to control infection. Because of the similarity in ultrastructural organization among spirochetes, knowledge gained from T. denticola can be applied to other spirochetes causing diseases in human and animals (syphilis, digital dermatitis, Lyme disease, relapsing fever, leptospirosis, etc.)

Electron Tomographic Studies of Mitochondrial Crista Topology: “Swirl” Mitochondria of Drosophila Flight Muscle

Extended abstract of a paper presented at Microscopy and Microanalysis 2007 in Ft. Lauderdale, Florida, USA, August 5 – August 9, 2007

Direct Observation of High-Temperature Polaronic Behavior In Colossal Magnetoresistive Manganites

The temperature dependence of the electronic and atomic structure of the colossal magnetoresistive oxides $La_{1-x}Sr_{x}MnO_{3}$ (x = 0.3, 0.4) has been studied using core and valence level photoemission, x-ray absorption and emission, and extended x-ray absorption fine structure spectroscopy. A dramatic and reversible change of the electronic structure is observed on crossing the Curie temperature, including charge localization and spin moment increase of Mn, together with Jahn-Teller distortions, both signatures of polaron formation. Our data are also consistent with a phase-separation scenario.Comment: 5 pages, 4 figures, revte

Evidence for Strong Itinerant Spin Fluctuations in the Normal State of CeFeAsO(0.89)F(0.11) Iron-Oxypnictides

The electronic structure in the normal state of CeFeAsO0.89F0.11 oxypnictide superconductors has been investigated with x-ray absorption and photoemission spectroscopy. All the data exhibit signatures of Fe d-electron itinerancy. Exchange multiplets appearing in the Fe 3s core level indicate the presence of itinerant spin fluctuations. These findings suggest that the underlying physics and the origin of superconductivity in these materials are likely to be quite different from those of the cuprate high-temperature superconductors. These materials provide opportunities for elucidating the role of magnetic fluctuations in high-temperature superconductivity.Comment: Shorter version. Accepted in Phys. Rev. Let

A pseudo-spectral approach to inverse problems in interface dynamics

An improved scheme for computing coupling parameters of the Kardar-Parisi-Zhang equation from a collection of successive interface profiles, is presented. The approach hinges on a spectral representation of this equation. An appropriate discretization based on a Fourier representation, is discussed as a by-product of the above scheme. Our method is first tested on profiles generated by a one-dimensional Kardar-Parisi-Zhang equation where it is shown to reproduce the input parameters very accurately. When applied to microscopic models of growth, it provides the values of the coupling parameters associated with the corresponding continuum equations. This technique favorably compares with previous methods based on real space schemes.Comment: 12 pages, 9 figures, revtex 3.0 with epsf style, to appear in Phys. Rev.

Sustainable but not spontaneous: Co-operatives and the solidarity funds in Italy

This paper aims to highlight the role of solidarity funds in the development and support of national co-operative movements. Those are financial institutions specialized in supporting the start-up and growth of co-operatives. By adopting a case study approach, our analysis shows that solidarity funds emerged globally with similar objectives. Our international comparison focuses on Italy but includes France, the United Kingdom and Québec as a specific Canadian province with a French institutional environment. Despite their crucial importance, there is limited available research on this subject. To this end, our paper has policy implications; we need to consider establishing such institutions in countries where co-operatives are lagging behind as traditional financial institutions are often unable to finance co-operatives because of their property rights regime

Electronic Structure of CeFeAsO1-xFx (x=0, 0.11/x=0.12) compounds

We report an extensive study on the intrinsic bulk electronic structure of the high-temperature superconductor CeFeAsO0.89F0.11 and its parent compound CeFeAsO by soft and hard x-ray photoemission, x-ray absorption and soft-x-ray emission spectroscopies. The complementary surface/bulk probing depth, and the elemental and chemical sensitivity of these techniques allows resolving the intrinsic electronic structure of each element and correlating it with the local structure, which has been probed by extended-x-ray absorption fine structure spectroscopy. The measurements indicate a predominant 4f1 (i.e. Ce3+) initial state configuration for Cerium and an effective valence-band-to-4f charge-transfer screening of the core hole. The spectra also reveal the presence of a small Ce f0 initial state configuration, which we assign to the occurrence of an intermediate valence state. The data reveal a reasonably good agreement with the partial density of states as obtained in standard density functional calculations over a large energy range. Implications for the electronic structure of these materials are discussed.Comment: Accepted for publication in Phys. Rev.

Engineered quantum tunnelling in extended periodic potentials

Quantum tunnelling from a tilted, but otherwise periodic potential is studied. Our theoretical and experimental results show that, by controlling the system's parameters, we can engineer the escape rate of a Bose-Einstein condensate to an exceptional degree. Possible applications of this atom-optics realization of the open Wannier-Stark system are discussed.Comment: 6 pp, proceedings DICE 11-15 September 2006, Castello di Piombino, Tuscany, Ital