Individual multiwall carbon nanotubes spectroscopy by scanning transmission X-ray microscopy

Scanning transmission X-ray microscopy (STXM) has been used to probe the electronic structure of individual multiwall carbon nanotubes by chemical mapping at the nanoscale. Carbon 1s near-edge X-ray absorption fine structure (NEXAFS) spectra of individual structures are shown to be able to differentiate carbon nanotubes from onionlike carbon nanoparticles and to differentiate nanotubes synthesized by different growth methods. Imaging of the very same region by both STXM and transmission electron microscopy is shown to be a very useful and complementary approach.     

Dust emission by powder handling: Influence of the hopper outlet on the dust plume

Dust generation in solids handling involving free fall of bulk materials and impacts on a stockpile can cause many problems in industry and be a great danger for operators health. This paper describes an experimental set up to characterize the dust plume formed in free fall of powders from a hopper and investigates the influence of various outlet geometries on the dust plume. For this purpose an image analysis technique was developed to quantify the characteristics of the dust plume.     

Optical properties of metallic nanowires by valence electron energy loss spectroscopy

The determination of intrinsic conductivity of nanowires (NWs) is essential to understand the charge transport behaviour involved in hybrid nanocomposites. These high conductive metallic fillers are good candidate to improve electrical properties of composites in aeronautic industry. The main difficulty is often to achieve the combination of both high spatial resolution and information on the physical properties as electrical conductivity. One of the suitable methods to give the desired information is electron energy loss spectroscopy (EELS) in scanning transmission electron microscopy (STEM) mode, especially in the low-loss region. This is demonstrated by studying the nickel and gold nanowire.     

Polarization dependence of the C 1s X-ray absorption spectra of individual multi-walled carbon nanotubes

The polarization dependence (linear dichroism) of the C 1s X-ray absorption spectrum of individual multi-walled carbon nanotubes (MWCNTs) is measured using scanning transmission X-ray microscopy. A very strong dichroic effect is found in the C 1s --> pi* transition, with almost complete disappearance of this transition when the electric-field (E)-vector is aligned parallel to high-quality (low-defect) MWCNTs and maximum intensity when the E-vector is orthogonal to the tube axis. In contrast, there is very little dichroism in the C 1s --> sigma* transitions. The origin of this polarization effect is explained. The magnitude of the polarization dependence is found to differ in MWCNTs synthesized by different methods (arc discharge versus chemical vapor deposition). This is ascribed to differences in densities of sp(2)-type defects. The potential for use of this signal to characterize defects in single-carbon-nanotube devices is discussed.     

Physicochemical characteristics and biological activities of seasonal atmospheric particulate matter sampling in two locations of Paris

Fine particulate matter present in urban areas seems to be incriminated in respiratory disorders. The aim of this study was to relate physicochemical characteristics of PM2.5 (particulate matter collected with a 50% efficiency for particles with an aerodynamic diameter of 2.5 microm) to their biological activities toward a bronchial epithelial cell line 16-HBE. Two seasonal sampling campaigns of particles were realized, respectively, in a kerbside and an urban background station in Paris. Sampled-PM2.5 mainly consist of particles with a size below 1 microm and are mainly composed of soot as assessed by analytical scanning electron microscopy. The different PM2.5 samples contrasted in their PAH content, which was the highest in the kerbside station in winter, as well as in their metal content. Kerbside station samples were characterized by the highest Fe and Cu content, which appears correlated to their hydroxyl radical generating properties measured by electron paramagnetic resonance. Particles were compared by their capacity to induce cytotoxicity, intracellular ROS production, and proinflammatory cytokine release (GM-CSF and TNF-alpha). At a concentration of 10 microg/cm2, all samples induced peroxide production and cytokine release to the similar extent in the absence of cytotoxicity. In conclusion, whereas the PM2.5 samples differ by their PAH and metal composition, they induce the same biological responses likely either due to components bioavailability and/ or interactions between PM components.     

Modeling of high voltage devices for ESD event simulation in SPICE

An ESD (electro-static-discharge) compact modeling methodology using a macro-modeling approach is introduced in this work for high voltage Lateral Double-diffused MOS (LDMOS) devices and new high-voltage protection clamps. The distinct characteristics of high voltage devices during high current/fast transient events are modeled without introducing convergence problems in ESD simulations for complex high voltage mixed-signal applications. The LDMOS ESD model consists of a sub-circuit that is built on top of the standard high-voltage MOS model (MOS20). The high voltage clamps, consisting of thyristor-type devices, are modeled using advanced bipolar junction transistor models.     

Differentiation of sCJD and vCJD forms by automated analysis of basal ganglia intensity distribution in multisequence MRI of the brain--definition and evaluation of new MRI-based ratios

We present a method for the analysis of basal ganglia (including the thalamus) for accurate detection of human spongiform encephalopathy in multisequence magnetic resonance imaging (MRI) of the brain. One common feature of most forms of prion protein diseases is the appearance of hyperintensities in the deep grey matter area of the brain in T2-weighted magnetic resonance (MR) images. We employ T1, T2, and Flair-T2 MR sequences for the detection of intensity deviations in the internal nuclei. First, the MR data are registered to a probabilistic atlas and normalized in intensity. Then smoothing is applied with edge enhancement. The segmentation of hyperintensities is performed using a model of the human visual system. For more accurate results, a priori anatomical data from a segmented atlas are employed to refine the registration and remove false positives. The results are robust over the patient data and in accordance with the clinical ground truth. Our method further allows the quantification of intensity distributions in basal ganglia. The caudate nuclei are highlighted as main areas of diagnosis of sporadic Creutzfeldt-Jakob Disease (sCJD), in agreement with the histological data. The algorithm permitted the classification of the intensities of abnormal signals in sCJD patient FLAIR images with a higher hypersignal in caudate nuclei (10/10) and putamen (6/10) than in thalami. Defining normalized MRI measures of the intensity relations between the internal grey nuclei of patients, we robustly differentiate sCJD and variant CJD (vCJD) patients, in an attempt to create an automatic classification tool of human spongiform encephalopathies.     

Short- and long-term dynamics of the toxic potential and genotypic structure in benthic populations of Microcystis

Microcystis colonies are known to overwinter on the surface of the sediment of freshwater ecosystems. However, little is known about the genotypic and toxicological dynamics of Microcystis populations during this benthic life stage. In this study, we report a two-year-long survey of benthic populations of Microcystis, which had spent from a few days to more than six years in the sediment. In order to avoid any interaction with the planktonic proliferations, we chose two deeply buried benthic populations, which could be easily dated. Quantitative PCR on mcyB gene and protein phosphatase inhibition assays were performed to measure their toxic potential, and their genotypic structure was assessed by Capillary Electrophoresis-Single Strand Conformation Polymorphism (CE-SSCP), based on 16S-23S Intergenic Transcribed Spacer (ITS). The microcystin content of the cells seemed to change sharply during the first few months of benthic survival, whereas this content was low and decreased steadily after several years of benthic life. No genetic selection was observed in either the proportion of potentially toxic clones or the ITS sequences for any of the populations considered. From these results, the benthic life stage of Microcystis appears to preserve the structure and the composition of the population over a far larger time scale than classical overwintering period. Finally, some genotypes were common in both of the benthic populations, even though they originated from planktonic blooms that had developed five years apart, suggesting a major overlap of planktonic proliferations in successive years.     

Access to High-Purity 7mG-cap RNA in Substantial Quantities by a Convenient All-Chemical Solid-Phase Method

Given the importance of mRNA with 5’-cap, easy access to RNA substrates with different ^7mG caps, of high quality and in large quantities is essential to elucidate the roles of RNA and the regulation of underlying processes. In addition to existing synthetic routes to 5’-cap RNA based on enzymatic, chemical or chemo-enzymatic methods, we present here an all-chemical method for synthetic RNA capping. The novelty of this study lies in the fact that the capping reaction is performed on solid-support after automated RNA assembly using commercial 2’-O-propionyloxymethyl ribonucleoside phosphoramidites, which enable final RNA deprotection under mild conditions while preserving both ^7mG-cap and RNA integrity. The capping reaction is efficiently carried out between a 5’-phosphoroimidazolide RNA anchored on the support and ^7mGDP in DMF in the presence of zinc chloride. Substantial amounts of ^7mG-cap RNA (from 1 to 28 nucleotides in length and of any sequence with or without internal methylations) containing various cap structures (^7mGpppA, ^7mGpppA_m, ^7mGppp^m6A, ^7mGppp^m6A_m, ^7mGpppG, ^7mGpppG_m) were obtained with high purity after IEX-HPLC purification. This capping method using solid-phase chemistry is convenient to perform and provides access to valuable RNA substrates as useful research tools to unravel specific issues regarding cap-related processes.