Search for the Standard Model Higgs -> gamma gamma decays with the ATLAS Detector at the LHC

International audienceA light Standard Model Higgs boson, with mass between 114 and ~150 GeV, is favored by precise measurements of electroweak radiative corrections and other theory predictions. One of the most important channels to search for this particle in the above mass region is the decay H-->gamma-gamma. This talk reviews the ATLAS discovery potential of a light Higgs boson in the two photon decay. In addition to the inclusive analysis we consider also the reconstruction of diphoton systems produced in association with jets. The studies are based on a realistic detector simulation of Monte Carlo signal and background events

Image compression using noncausal prediction

Image compression commonly is achieved using prediction of the value of pixels from surrounding pixels. Normally the choice of pixels used in the prediction is restricted to previously scanned pixels. A better prediction can be achieved if pixels on all sides of the pixel to be predicted are used. A prediction and decoding method is proposed that is independent of scanning order of the image. The decoding process makes use of an iterative decoder. A sequence of images is generated that converges to a final image that is identical to the original image. The theory underlying noncausal prediction and iterative decoding is developed. Convergence properties of the decoding algorithm are studied and conditions for convergence are presented. Distortions to the prediction residual after encoding can be caused by storage requirements, such as quantization and compression and also by errors in transmission. Effects of distortions of the residual on the final decoded image are investigated by introducing several types of distortion of the residual, including (1) alteration of randomly selected bits in the residual, (2) addition of a sinusoidal signal to the residual, (3) quantization of the residual and (4) compression of the residual using lossy Haar wavelet coding. The resulting distortion in the decoded images was generally less for noncausal prediction than for causal prediction, both in terms of PSNR and visual quality. Most noticeably, the streaks found in the decoded Image after causal encoding were absent with noncausal encoding

Cognitive mapping of organic vegetable production in Flanders to support farmers strategy design

Organic farmers inherently have to cope with complex agricultural production system processes. Next to pursuing economic performance, farm management also encompasses optimization of the farm's ecological and social performance. The question arises how to maintain a certain balance between the multiple purposes. For this consideration, farmers as well as researchers need to have a good understanding of the whole farm functioning. Therefore this study aims to model the factors and their inter-relations influencing an organic farmers' decision-making process. These factors and inter-relations were modelled by using the qualitative cognitive mapping technique. Cognitive mapping can be used to develop maps of socio-ecological systems based on people's knowledge of ecosystems. Different stakeholders (farmers and experts) were interviewed in order to represent and visualize their tacit knowledge. Through in-depth interviews, stakeholders were questioned on the critical success factors of organic farm management and how these factors relate to each other. Based on these interviews, individual cognitive maps were constructed which were subsequently merged to build a social cognitive map. The social cognitive map represents the stakeholders' perception of the agricultural production system. It covers a broad range of factors (economic, agro-technical and biophysical factors, next to a few social factors), of which the most central ones are crop choice, crop rotation, marketing and technology and mechanization

Pressure-induced amorphization and polyamorphism in one-dimensional single crystal TiO2 nanomaterials

The structural phase transitions of single crystal TiO2-B nanoribbons were investigated in-situ at high-pressure using the synchrotron X-ray diffraction and the Raman scattering. Our results have shown a pressure-induced amorphization (PIA) occurred in TiO2-B nanoribbons upon compression, resulting in a high density amorphous (HDA) form related to the baddeleyite structure. Upon decompression, the HDA form transforms to a low density amorphous (LDA) form while the samples still maintain their pristine nanoribbon shape. HRTEM imaging reveals that the LDA phase has an {\alpha}-PbO2 structure with short range order. We propose a homogeneous nucleation mechanism to explain the pressure-induced amorphous phase transitions in the TiO2-B nanoribbons. Our study demonstrates for the first time that PIA and polyamorphism occurred in the one-dimensional (1D) TiO2 nanomaterials and provides a new method for preparing 1D amorphous nanomaterials from crystalline nanomaterials.Comment: 4 figure

A Study of the Formation of Single- and Double-Walled Carbon Nanotubes by a CVD Method

The reduction in H2/CH4 atmosphere of aluminum-iron oxides produces metal particles small enough to catalyze the formation of single-walled carbon nanotubes. Several experiments have been made using the same temperature profile and changing only the maximum temperature (800-1070 °C). Characterizations of the catalyst materials are performed using notably 57Fe Mo¨ssbauer spectroscopy. Electron microscopy and a macroscopical method are used to characterize the nanotubes. The nature of the iron species (Fe3+, R-Fe, ç-Fe-C, Fe3C) is correlated to their location in the material. The nature of the particles responsible for the high-temperature formation of the nanotubes is probably an Fe-C alloy which is, however, found as Fe3C by postreaction analysis. Increasing the reduction temperature increases the reduction yield and thus favors the formation of surface-metal particles, thus producing more nanotubes. The obtained carbon nanotubes are mostly single-walled and double-walled with an average diameter close to 2.5 nm. Several formation mechanisms are thought to be active. In particular, it is shown that the second wall can grow inside the first one but that subsequent ones are formed outside. It is also possible that under given experimental conditions, the smallest (<2 nm) catalyst particles preferentially produce double-walled rather than single-walled carbon nanotubes

Hydrogen production during the irradiation of gaseous organic compounds: advantage of an extracted beam

ACE, Accélérateur, NIMBInternational audienceThis paper presents a fundamental study of the radiolysis of gaseous organic molecules induced by proton beam. For that purpose, a specific extracted beam line associated with a gas irradiation cell was set up on the 4 MV facility of the Institut de Physique Nucléaire of Lyon. The first experiments have been performed with gaseous alkanes and alkenes. The gaseous species formed during irradiation are analysed by an on-line gas chromatography instrument equipped with two detectors. In order to test our experimental faiclity, we have studied the influence of irradiation parameters (duration, beam intensity, pressure) on the production of hydrogen. In the case of propane, the radiolytic yield value of hydrogen G(H$_2$) is equal to 3.7 for total does in the range of 0.4 to 2.3 MGy at atmospheric pressure

Investigation of four-year chemical composition and organic aerosol sources of submicron particles at the ATOLL site in northern France

This study presents the first long-term online measurements of submicron (PM1) particles at the ATOLL (ATmospheric Observations in liLLe) platform, in northern France. The ongoing measurements using an Aerosol Chemical Speciation Monitor (ACSM) started at the end of 2016 and the analysis presented here spans through December 2020. At this site, the mean PM1 concentration is 10.6 μg m-3, dominated by organic aerosols (OA, 42.3%) and followed by nitrate (28.9%), ammonium (12.3%), sulfate (8.6%), and black carbon (BC, 8.0%). Large seasonal variations of PM1 concentrations are observed, with high concentrations during cold seasons, associated with pollution episodes (e.g. over 100 μg m-3 in January 2017). To study OA origins over this multiannual dataset we performed source apportionment analysis using rolling positive matrix factorization (PMF), yielding two primary OA factors, a traffic-related hydrocarbon-like OA (HOA) and biomass-burning OA (BBOA), and two oxygenated OA (OOA) factors. HOA showed a homogeneous contribution to OA throughout the seasons (11.8%), while BBOA varied from 8.1% (summer) to 18.5% (winter), the latter associated with residential wood combustion. The OOA factors were distinguished between their less and more oxidized fractions (LO-OOA and MO-OOA, on average contributing 32% and 42%, respectively). During winter, LO-OOA is identified as aged biomass burning, so at least half of OA is associated with wood combustion during this season. Furthermore, ammonium nitrate is also a predominant aerosol component during cold-weather pollution episodes - associated with fertilizer usage and traffic emissions. This study provides a comprehensive analysis of submicron aerosol sources at the recently established ATOLL site in northern France from multiannual observations, depicting a complex interaction between anthropogenic and natural sources, leading to different mechanisms of air quality degradation in the region across different seasons

Toward an Anthropology of Mathematizing

This essay investigates the practical ways that artists and craftspeople cultivate mathematical sensibilities through their practical immersion in making and problem-solving. Mathematical sensibilities refer to skilled kinds of perception and heightened levels of attention and discernment regarding the qualitative properties of an object or composition, such as its shape, proportion, balance, symmetry, centredness, alignment or levelness. It also includes an ‘intuitive’ quantitative sense of volume, mass, weight, thickness and dimension. The objective of the investigation is not to describe the ways that a maker’s existing knowledge and training in formal mathematics is put into practice, but rather to elucidate the ways that their practices of making produce kinds of ‘non-formalised’, context-dependent mathematical understanding and knowledge. The starting point for exploring embodied mathematizing is therefore not from the cognitive or neurosciences, psychology or formal mathematics, it is argued, but rather from a phenomenological approach – ‘an opening on the world’ – that attends to person, materials, tools and other physical and qualitative features that make up the total environment in which activity unfolds