Experimental and theoretical approaches to the study of TMI-zeolite (TM = Fe, Co, Cu)

Transition metal ions in zeolites TMI-zeolite (TM = Fe, Co, Cu) attract great attention due to their potentialities as catalysts. In the recent years, the high efficiency of TMI-zeolites for the selective catalytic reduction (SCR) of contaminated flue gases has been demonstrated. It has been shown that the structure of the framework, the nature and location of extraframework cation species play a fundamental role in the process. Experimental results based on spectroscopies, as well as on reactivity studies have led to valuable insights about the structure of cationic sites as well as about the active species involved during the catalytic reactions. However, it is not sufficient to obtain all this information. This review reporting density functional theory (DFT) calculations shows that a molecular approach is very useful and has become an indispensable tool for the determination of the geometries, the electronic structures, the spectroscopic properties and the reactivity of TMI-zeolites.     

Influence of oxygen on phase transformations in a Ti-48 At. pct Al alloy

The composition and structure of Ti-48 at. pct Al alloys with various oxygen contents, quenched from a homogeneous α state, have been studied by means of one-dimensional atom-probe (1DAP) and transmission electron microscopy (TEM) analysis. Two regimes are observed. The change from one regime to the other depends on the global oxygen content. If the oxygen content is lower than 1.2 at. pct, the α→γ _m massive transformation is involved during the quench. The alloys, hence, exhibit massive γ _m-structure regions and regions having a two-phase (α ₂+γ) ultrafine lamellar structure. Very thin α ₂ plates, saturated with oxygen, are observed in γ _m regions. The precipitation of these α ₂ plates is promoted by excess oxygen in the γ _m structure. Within ultra-fine lamellar-structure regions, oxygen is concentrated in α ₂ lamellae (not saturated with oxygen) and is found to be responsible for the high volume fraction of α ₂ phase. When the oxygen content is larger than 1.2 at. pct, the massive transformation is suppressed and the ultrafine lamellar structure is only observed in quenched samples. Analysis of the α → α ₂ chemical ordering in the classical lamellar structure, formed within the (α+γ) dual-phase field, shows that high oxygen contents favor the chemical-ordering reaction of α phase at high temperatures (e.g., 1423 and 1523 K). It has, hence, been inferred that, above 1.2 at. pct O, the α → γ _m massive transformation is suppressed and replaced by the α → α ₂+y transformation paths. This article is based on a presentation made in the symposium entitled “Fundamentals of Structural Intermetallics,” presented at the 2002 TMS Annual Meeting, February 21–27, 2002, in Seattle, Washington, under the auspices of the ASM and TMS Joint Committee on Mechanical Behavior of Materials.     

Worker flexibility and its perceived contribution to performance: The moderating role of task characteristics

This study examined the relationship between worker flexibility in team‐based work and its perceived contribution to efficiency, work quality, and innovation, and the moderating role of task autonomy, skill utilization, and task monotony. Four‐hundred ninety‐four employees from 113 teams in 15 organizations completed and returned questionnaires. Skill utilization proved to be positively related to perceived contribution of flexibility to efficiency, work quality, and innovation. Furthermore, skill utilization strengthened the positive relationships between worker flexibility and its perceived contribution to efficiency and work quality and weakened the negative relationship between worker flexibility and its perceived impact on innovation. Task monotony was negatively related to the perceived quality benefits of being flexible. In addition, it weakened the positive relationship between worker flexibility and its perceived contribution to both efficiency and quality and strengthened the negative relationship with the perceived impact of flexibility on innovation. Task autonomy was positively related to the perceived contribution of flexibility to innovation and weakened the negative relationship between worker flexibility and the perceived innovation benefits of being flexible. The authors conclude that skill utilization and lack of monotony are important issues in relation to worker flexibility on all performance objectives that were considered, whereas task autonomy seems especially relevant when innovation is a key issue. © 2007 Wiley Periodicals, Inc. Hum Factors Man 17: 117–135, 2007.     

Synthesis of few-layer graphene via microwave plasma-enhanced chemical vapour deposition

If graphene is ever going to live up to the promises of future nanoelectronic devices, an easy and cheap route for mass production is an essential requirement. A way to extend the capabilities of plasma-enhanced chemical vapour deposition to the synthesis of freestanding few-layer graphene is presented. Micrometre-wide flakes consisting of four to six atomic layers of stacked graphene sheets have been synthesized by controlled recombination of carbon radicals in a microwave plasma. A simple and highly reproducible technique is essential, since the resulting flakes can be synthesized without the need for a catalyst on the surface of any substrate that withstands elevated temperatures up to 700?°C. A thorough structural analysis of the flakes is performed with electron microscopy, x-ray diffraction, Raman spectroscopy and scanning tunnelling microscopy. The resulting graphene flakes are aligned vertically to the substrate surface and grow according to a three-step process, as revealed by the combined analysis of electron microscopy and x-ray photoelectron spectroscopy.     

Study of Fullerenes,Nanotubes and Nanowires by Transmission Electron Microscopy

Abstract

The arc discharge reactor developped by Kratschmer et al^l produces a variety of new carbonaceous solids, including fullerenes and different kinds of graphitic cages of nanometric size, which can be hollow or filled with various materials. Complementary to neutron and X ray diffraction techniques, transmission electron microscopy rapidly appeared among the most important techniques for studying the structures of fullerenes and fullerites^2?6. Very generally, it allows us to obtain diffraction patterns of micronic size crystallites and the different imaging modes provide an unique tool to investigate in real space the morphology of the crystallites, structural defects faults at microscopic and nanometric scales^6?8. It is possible to perform very local chemical analysis and to study chemical environments in order to determine the nature of chemical bonds⁹. Futhermore, it is possible to study phase transitions through in situ experiments^5,10–12 and the behaviour of fullerites upon electron irradiation¹³. The interest of this technique has appeared even more crucial with the discovery of narotubes¹⁴ and their ability to be filled¹⁵ since, because of their nanometric size, the electron microscopy is at the moment the unique tool allowing their study and is therefore a challenge in the development of these new materials for applications in nanotechnology.     

Improved bound for stochastic formal correctness of numerical algorithms

We provide bounds on the probability that accumulated errors were never above a given threshold on numerical algorithms. Such algorithms are used, for example, in aircraft and nuclear power plants. This report contains simple formulas based on Lévy’s, Markov’s and Hoeffding’s inequalities and it presents a formal theory of random variables with a special focus on producing concrete results. We select three very common applications that cover the common practices of systems that evolve for a long time. We compute the number of bits that remain continuously significant in the first two applications with a probability of failure around one out of a billion, where worst case analysis considers that no significant bit remains. We are using PVS as such formal tools force explicit statement of all hypotheses and prevent incorrect uses of theorems.     

Dihydrosphingosine-Induced Programmed Cell Death in Tobacco BY-2 Cells Is Independent of H2O2 Production

Sphinganine or dihydrosphingosine (d18:0,DHS),one of the most abundant free sphingoid Long Chain Base (LCB) in plants,has been recently shown to induce both cytosolic and nuclear calcium transient increases and a correlated Programmed Cell Death (PCD) in tobacco BY-2 cells. In this study,in order to get deeper insight into the LCB signaling pathway leading to cell death,the putative role of Reactive Oxygen Species (ROS) has been investigated. We show that DHS triggers a rapid dose-dependent production of H2O2 that is blocked by diphenyleniodonium (DPI),indicating the involvement of NADPH oxidase(s) in the process. In addition,while DPI does not block DHS-induced calcium increases,the ROS production is inhibited by the broad spectrum calcium channel blocker lanthanum (La3+). Therefore,ROS production occurs downstream of DHS-induced Ca2+ transients. Interestingly,DHS activates expression of defense-related genes that is inhibited by both La3+ and DPI. Since DPI does not prevent DHS-induced cell death,these results strongly indicate that DHS-induced H2O2 production is not implicated in PCD mechanisms but rather would be associated to basal cell defense mechanisms.     

Benefits of the Combined Use of Immunological- and PCR-Based Methods for Determination of Staphylococcal Enterotoxin Food Safety Criteria in Cheeses

The aim of this study, performed under official controls, was to assess the relationship between the content of staphylococcal enterotoxins SEA to SEE in cheese samples and the enterotoxigenic potential of Staphylococcus aureus isolates. The level of correlation may further underline the benefit of using complementary approaches based on immunological tests and the PCR method to improve the diagnosis for determination of staphylococcal enterotoxin food safety criteria in cheeses submitted to official controls and own checks.     

The AETL methodology as a potential solution to current challenges associated with the development and use of acute exposure levels in Seveso II applications

This paper analyses current trends in the development and use of acute exposure levels in Europe for the implementation of the Seveso II Directive [Council Directive 96/82/EC of December 9, 1996 on the control of major-accident hazards involving dangerous substances. Official Journal of the European Communities, vol. L 10, January 14, 1997, Luxembourg, pp. 13-33]. It also describes a new initiative to develop a European methodology for deriving acute exposure threshold levels that responds to emerging needs in this area. The need for acute exposure values to predict human health effects of potential accidents on exposed populations has burgeoned in recent years. As the driving legislation for managing industrial hazards in Europe, the Seveso II Directive has particularly influenced this trend. Yet at this time it is questionable whether the availability and range of acute exposure values for toxic substances has kept apace with the growing need. Results of a survey of Seveso II competent authorities in the EU-15 revealed that a variety of different types of acute exposure values (AEGLs, EPRGs, etc.) are used for Seveso II applications. Moreover, a comparison of these values indicates gaps in coverage of substances as well as inconsistencies in terms of how health effects and exposure periods are defined for each type. These findings highlight an opportunity for greater collaboration on scientific inputs to application of the Directive in Europe. The ACUTEX project is an EU-funded research project aimed at furthering scientific exchange and collaboration in support of the development of acute exposure levels for toxic substances in Europe. Its goal is to develop a European methodology for deriving acute exposure threshold levels (AETLs). In particular, it provides the possibility for a common European platform for developing additional acute exposure values to meet emerging needs and cover more chemical substances. To maximise success, the work plan is designed to meet two very important challenges, the need to complement and add value to the existing array of acute exposure methodologies and the necessity of meeting requirements of a diverse range of European stakeholders. As such the project will draw on collaboration among European scientists and process of deliberation among stakeholders to deliver the following key results: (1) to facilitate wide acceptance of the methodology in Europe by both the scientific community and communities of different end-users; (2) to provide greater equivalence and transparency in implementation of the Seveso II Directive across the Member States, specifically through the development of common scientific bases for assessing risks and making risk management decisions related to toxic releases; (3) to produce a methodology that remains open to future collaboration on derivation of acute exposure levels on a European and a global basis.