Off-axis electron holography of bacterial cells and magnetic nanoparticles in liquid

The mapping of electrostatic potentials and magnetic fields in liquids usingelectron holography has been considered to be unrealistic. Here, we showthat hydrated cells ofMagnetospirillum magneticumstrain AMB-1 and assem-blies of magnetic nanoparticles can be studied using off-axis electronholography in a fluid cell specimen holder within the transmission electronmicroscope. Considering that the holographic object and reference waveboth pass through liquid, the recorded electron holograms show sufficientinterference fringe contrast to permit reconstruction of the phase shift ofthe electron wave and mapping of the magnetic induction from bacterialmagnetite nanocrystals. We assess the challenges of performingin situmagne-tization reversal experiments using a fluid cell specimen holder, discussapproaches for improving spatial resolution and specimen stability, and outlinefuture perspectives for studying scientific phenomena, ranging from interpar-ticle interactions in liquids and electrical double layers at solid–liquidinterfaces to biomineralization and the mapping of electrostatic potentialsassociated with protein aggregation and folding

Guest Editorial Special Issue on Medical Imaging and Image Computing in Computational Physiology

International audienceThe January 2013 Special Issue of IEEE transactions on medical imaging discusses papers on medical imaging and image computing in computational physiology. Aslanid and co-researchers present an experimental technique based on stained micro computed tomography (CT) images to construct very detailed atrial models of the canine heart. The paper by Sebastian proposes a model of the cardiac conduction system (CCS) based on structural information derived from stained calf tissue. Ho, Mithraratne and Hunter present a numerical simulation of detailed cerebral venous flow. The third category of papers deals with computational methods for simulating medical imagery and incorporate knowledge of imaging physics and physiology/biophysics. The work by Morales showed how the combination of device modeling and virtual deployment, in addition to patient-specific image-based anatomical modeling, can help to carry out patient-specific treatment plans and assess alternative therapeutic strategies

Thermopower in the strongly overdoped region of single-layer Bi2Sr2CuO6+d superconductor

The evolution of the thermoelectric power S(T) with doping, p, of single-layer Bi2Sr2CuO6+d ceramics in the strongly overdoped region is studied in detail. Analysis in term of drag and diffusion contributions indicates a departure of the diffusion from the T-linear metallic behavior. This effect is increased in the strongly overdoped range (p~0.2-0.28) and should reflect the proximity of some topological change.Comment: 4 pages, 4 figure

Anomalous electronic susceptibility in Bi2Sr2CuO6+d and comparison with other overdoped cuprates

We report magnetic susceptibility performed on overdoped Bi2Sr2CuO6+d powders as a function of oxygen doping d and temperature T. The decrease of the spin susceptibility with increasing T is confirmed. At sufficient high temperature, the spin susceptibility Chi_s presents an unusual linear temperature dependence Chi_s ~ Chi_s0 -Chi_1 T. Moreover, a linear correlation between Chi_1 and Chi_s0 for increasing hole concentration is displayed. A temperature Tchi, independent of hole doping characterizes this scaling. Comparison with other cuprates of the literature(LSCO, Tl-2201 and Bi-2212), over the same overdoped range, shows similarities with above results. These non conventional metal features will be discussed in terms of a singular narrow-band structure.Comment: 16 pages, 4 figure

Results of the French Evalda-Media evaluation campaign for literal understanding

International audienceThe aim of the MEDIA-EVALDA project is to evaluate the understanding capabilities of dialog systems. This paper presents the MEDIA protocol for speech understanding evaluation and describes the results of the June 2005 literal evaluation campaign. Five systems, both symbolic or corpus-based participated to the evaluation which is based on a common semantic representation. Different scorings have been performed on the system results. The understanding error rate, for the Full scoring is, depending on the systems, from 29% to 41.3%. A diagnosis analysis of these results is proposed

Efficient depth estimation using trinocular stereo

Journal ArticleWe present recent advancements in our passive trinocular stereo system. These include a technique for calibrating and rectifying in a very efficient and simple manner the triplets of images taken for trinocular stereovision systems. After the rectification of images, epipolar lines are parallel to the axes of the image coordinate frames. Therefore, potential matches between the three images satisfy simpler relations, allowing for a less complicated and more efficient matching algorithm. We also describe a more robust and general control strategy now employed in our trinocular stereo system. We have also developed an innovative method for the reconstruction of 3-D segments which provides better results and a new validation technique based on the observation that neighbors in the image should be neighbors in space. Experiments are presented demonstrating these advancements

Optical properties of an effective one-band Hubbard model for the cuprates

We study the Cu and O spectral density of states and the optical conductivity of CuO_2 planes using an effective generalized one-band Hubbard model derived from the extended three-band Hubbard model. We solve exactly a square cluster of 10 unit cells and average the results over all possible boundary conditions, what leads to smooth functions of frequency. Upon doping, the Fermi energy jumps to Zhang-Rice states which are connected to the rest of the valence band (in contrast to an isolated new band in the middle of the gap). The transfer of spectral weight depends on the parameters of the original three-band model not only through the one-band effective parameters but also through the relevant matrix elements. We discuss the evolution of the gap upon doping. The optical conductivity of the doped system shows a mid-infrared peak due to intraband transitions, a pseudogap and a high frequency part related to interband transitions. Its shape and integrated weight up to a given frequency (including the Drude weight) agree qualitatively with experiments in the cuprates for low to moderate doping levels, but significant deviations exist for doping $x>0.3$.Comment: 11 pages (tex), 14 figures (ps

A process very similar to multifractional Brownian motion

In Ayache and Taqqu (2005), the multifractional Brownian (mBm) motion is obtained by replacing the constant parameter $H$ of the fractional Brownian motion (fBm) by a smooth enough functional parameter $H(.)$ depending on the time $t$. Here, we consider the process $Z$ obtained by replacing in the wavelet expansion of the fBm the index $H$ by a function $H(.)$ depending on the dyadic point $k/2^j$. This process was introduced in Benassi et al (2000) to model fBm with piece-wise constant Hurst index and continuous paths. In this work, we investigate the case where the functional parameter satisfies an uniform H\"older condition of order \beta>\sup_{t\in \rit} H(t) and ones shows that, in this case, the process $Z$ is very similar to the mBm in the following senses: i) the difference between $Z$ and a mBm satisfies an uniform H\"older condition of order $d>\sup_{t\in \R} H(t)$; ii) as a by product, one deduces that at each point $t\in \R$ the pointwise H\"older exponent of $Z$ is $H(t)$ and that $Z$ is tangent to a fBm with Hurst parameter $H(t)$.Comment: 18 page