For a better estimation of gamma heating in nuclear material-testing reactors and associated devices: status and work plan from calculation methods to nuclear data

The determination of gamma heating levels in material-testing reactors (MTRs) is of crucial importance as gamma heating affects both safety and performance parameters of MTRs [1 Amharrak H, Di Salvo J, Lyoussi A, Carette M, Reynard-Carette C. State of the art on nuclear heating in a mixed (n/gamma) field in research reactors. Nucl Instrum Methods A. 2014;749:57–67.[Crossref], [Web of Science ®] , [Google Scholar],2 Brun J, Reynard-Carette C, Lyoussi A, Merroun O, Carette M, Janulyte A, Zerega Y, Andre J, Bignan G, Chauvin J-P, Fourmentel D, Gonnier C, Guimbal P, Malo J-Y, Villard J-F. Numerical and experimental calibration of calorimetric sample cell dedicated to nuclear heating measurements. IEEE Trans Nucl Sci. 2012;59:3173–3179.[Crossref], [Web of Science ®] , [Google Scholar]]. The required accuracy (5% at one standard deviation) makes it necessary to calibrate bias and uncertainty associated with MTR gamma-heating calculations. Main steps of bias determination for gamma-heating calculations include, first, the development of a calculation methodology with the controlled use of physical approximations; second, the interpretation of gamma-heating measurements with reference calculations so as to determine bias supposed to be mainly due to nuclear data.     

Carbon nanotube synthesis: from large-scale production to atom-by-atom growth

The extraordinary electronic, thermal and mechanical properties of carbon nanotubes (CNTs) closely relate to their structure. They can be seen as rolled-up graphene sheets with their electronic properties depending on how this rolling up is achieved. However, this is not the way they actually grow. Various methods are used to produce carbon nanotubes. They all have in common three ingredients: (i) a carbon source, (ii) catalyst nanoparticles and (iii) an energy input. In the case where the carbon source is provided in solid form, one speaks about 'high temperature methods' because they involve the sublimation of graphite which does not occur below 3200?°C. The first CNTs were synthesized by these techniques. For liquid or gaseous phases, the generic term of 'medium or low temperature methods' is used. CNTs are now commonly produced by these latter techniques at temperatures ranging between 350 and 1000?°C, using metal nanoparticles that catalyze the decomposition of the gaseous carbon precursor and make the growth of nanotubes possible. The aim of this review article is to give a general overview of all these methods and an understanding of the CNT growth process.     

High temperature activation and deactivation of single-walled carbon nanotube growth investigated by in situ Raman measurements

A decrease of nanotube yield is usually observed at high temperature. Here, we report on the origins of the activation and deactivation of the SWCNT growth in this high temperature range (between 700 °C and 850 °C) based on in situ Raman measurements. We observed that, at high temperature, carbon precursors such as ethanol and methane readily reduce metal oxide such as Co₃O₄. Once reduced, the size distribution of the catalyst particles quickly evolves at high temperature leading to a dramatic deactivation of the nanotube growth. An oxidizing pre-treatment has a stabilizing effect on the catalyst. In addition, we evidenced a threshold partial pressure of the carbon precursor to initiate the growth. This threshold partial pressure sets a second requirement for activating the nanotube growth in addition to the requirement of reducing the catalyst.     

Where Is the Organization Looking in Order to Be Proactive about Safety? A Framework for Revealing whether It Is Mostly Looking Back,Also Looking Forward or Simply Looking Away

Despite the desire to utilize proactive safety metrics, research results indicate imbalances can arise between economic performance metrics and safety metrics. Imbalances can arise, first, because there are fewer proactive metrics available relative to the data an organization can compile to build reactive metrics. Second, there are a number of factors that lead organizations to discount proactive metrics when they conflict with shorter‐term and more definitive reactive metrics. This paper introduces the Q4‐Balance Framework to analyse economy‐safety trade‐offs. Plotting the sets of metrics used by an organization in the four‐quadrant visualization can be used to identify misalignments, overlap and false diversity. It results in a visualization of the set of metrics an organization uses and where these conflict or reinforce each other. The framework also provides a way to assess an organization's safety energy as a kind of analysis of an organization's capability to be proactive about safety.     

Explainability of Deep Vision-Based Autonomous Driving Systems: Review and Challenges

International Journal of Computer Vision - This survey reviews explainability methods for vision-based self-driving systems trained with behavior cloning. The concept of explainability has several...     

Beyond REACH: Roadblocks and shortcuts en route to integrated risk assessment and management of chemicals

This paper addresses obstacles and opportunities for the development and application of novel methods for integrated assessment of cumulative risks from chemicals, exemplified by the REACH legislation of the EU, in the context of multiple stressors and of chemicals policy. We examine the role of such methods in connection with REACH by models of integration and innovation of risk information in multi-actor risk governance; analyses of key documents on REACH; and interviews with EU regulators and stakeholders. We first explain the emergence of REACH as a response to tensions in EU chemicals, environmental and other policies. We then analyze the present configuration of REACH particularly in relation to key dimensions of risk integration: across stressors; exposed organisms; and impacts. Among the policy aspects of integrated risk information, we focus on its interaction with management and the contesting framings and interpretations of assessment. Avenues and barriers are identified for integrated treatment of risks under REACH and with other instruments. We emphasize how bounded, formal and static assessments interact with open and informal approaches that have more flexibility in integrating risks in new ways. We conclude with a generalizing discussion on the role of novel methods of integrated risk assessment in the development of reflexive and participatory governance under REACH and beyond.     

The influence of molar mass on rheological and dilute solution properties of poly(butylene succinate)

The fundamental rheological properties of a wide molar mass M_w range of poly(butylene succinate)s (PBSs) are investigated. For entangled samples and a reference temperature of 140°C, the shear viscosity is described by the Carreau–Yasuda model. The plateau modulus is estimated at 1.5 × 10⁵ Pa, the average activation energy of PBS melt is , and the critical molar mass for entanglement M_c is found to be 16,000 g mol^?1 (PS equivalent). The dilute solution properties of PBS are also studied. A size exclusion chromatography equipped with a triple detection system is used to estimate the Mark–Houwink–Sakurada (MHS) parameters of PBS in solution in chloroform at 30°C. The exponent a and the coefficient K of the MHS relationship are found to be 0.71 ± 0.1 and 39.94 × 10^?5 ± 6.31 × 10^?5 dL g^?1(g mol^?1)^?a, respectively. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40887.     

Electron diffraction analysis of individual single-walled carbon nanotubes

We present a detailed electron diffraction study of individual single-walled carbon nanotubes. A novel sample preparation procedure provides well-separated, long and straight individual single-shell nanotubes. Diffraction experiments are carried out at 60 kV, below the threshold for knock-on damage in carbon nanotubes. We describe experimental parameters that allow single-tube electron diffraction experiments with widely available thermal emission transmission electron microscopes. Further, we review the simulation of diffraction patterns for these objects.     

Variable temperature characterization of N,N′-Bis(n-pentyl)terrylene-3,4:11,12-tetracarboxylic diimide thin film transistor

Organic thin film transistors (OTFT) based on N,N′-Bis(n-pentyl)terrylene-3,4:11,12-tetracarboxylic diimide (TTCDI-5C) with Al or Au top-contact electrodes were deposited on SiO₂ (200 nm)/p-Si (0 0 1) substrates. Carrier mobility was examined as a function of temperature in the range from 50 to 310 K. Two distinct carrier transfer behaviours were observed: temperature independent behaviour below 150 K and thermally activated behaviour above 150 K. Activation energies presented values of 85–130 meV depending on the metal electrodes (Au, Al), which can be attributed to the carrier traps at the interface and the energy-level offset between the lowest unoccupied molecular orbital (LUMO) and the work functions of the respective metals.