Positron production in crossed beams of bare uranium nuclei

Positron creation in crossed-beam collisions of high-energy, fully stripped heavy ions is investigated within the coupled-channel formalism. In comparison with fixed-target collisions of highly stripped heavy-ion projectiles positron production probabilities are enhanced by more than one order of magnitude. The increase results from the possibility to excite electrons from the negative energy continuum into all bound states. The positron spectrum is shifted towards higher energies because of the absence of electron screening. Rutherford scattering as well as nuclear collisions with time delay are investigated. We also discuss the filling of empty bound states by electrons from pair-production processes

Electron emission and positron production in deep inelastic heavy-ion reactions

Atomic excitations are used to obtain information on the course of a nuclear reaction. Employing a semiclassical picture we calculate the emission of δ electrons and positrons in deep inelastic nuclear reactions for the example of U+U collisions incorporating nuclear trajectories resulting from two different nuclear friction models. The emission spectra exhibit characteristic deviations from those expected for elastic Coulomb scattering. The theoretical probabilities are compared with recent experimental data by Backe et al. A simple model is used to estimate the influence of a threebody breakup of the compound system upon atomic excitations

Energy cost and machine learning accuracy impact of k-anonymisation and synthetic data techniques

To address increasing societal concerns regarding privacy and climate, the EU adopted the General Data Protection Regulation (GDPR) and committed to the Green Deal. Considerable research studied the energy efficiency of software and the accuracy of machine learning models trained on anonymised data sets. Recent work began exploring the impact of privacy-enhancing techniques (PET) on both the energy consumption and accuracy of the machine learning models, focusing on k-anonymity. As synthetic data is becoming an increasingly popular PET, this paper analyses the energy consumption and accuracy of two phases: a) applying privacy-enhancing techniques to the concerned data set, b) training the models on the concerned privacy-enhanced data set. We use two privacy-enhancing techniques: k-anonymisation (using generalisation and suppression) and synthetic data, and three machine-learning models. Each model is trained on each privacy-enhanced data set. Our results show that models trained on k-anonymised data consume less energy than models trained on the original data, with a similar performance regarding accuracy. Models trained on synthetic data have a similar energy consumption and a similar to lower accuracy compared to models trained on the original data.Comment: Published in the proceedings (Pages: 57-65) of The International Conference on Information and Communications Technology for Sustainability (ICT4S) 2023 in Rennes, France. 9 pages, 4 figures, 5 table

Spatial and temporal distribution of atmospheric aerosols in the lowermost troposphere over the Amazonian tropical rainforest

International audienceWe present measurements of aerosol physico-chemical properties below 5 km altitude over the tropical rain forest and the marine boundary layer (MBL) obtained during the LBA-CLAIRE 1998 project. The MBL aerosol size distribution some 50-100km of the coast of French Guyana and Suriname showed a bi-modal shape typical of aged and cloud processed aerosol. The average particle number density in the MBL was 383cm-3. The daytime mixed layer height over the rain forest for undisturbed conditions was estimated to be between 1200-1500m. During the morning hours the height of the mixed layer increased by 144-180mh-1. The median daytime aerosol number density in the mixed layer increased from 450cm-3 in the morning to almost 800cm-3 in the late afternoon. The evolution of the aerosol size distribution in the daytime mixed layer over the rain forest showed two distinct patterns. Between dawn and midday, the Aitken mode particle concentrations increased, whereas later during the day, a sharp increase of the accumulation mode aerosol number densities was observed, resulting in a doubling of the morning accumulation mode concentrations from 150cm-3 to 300cm-3. Potential sources of the Aitken mode particles are discussed here including the rapid growth of ultrafine aerosol particles formed aloft and subsequently entrained into the mixed layer, as well as the contribution of emissions from the tropical vegetation to Aitken mode number densities. The observed increase of the accumulation mode aerosol number densities is attributed to the combined effect of: the direct emissions of primary biogenic particles from the rain forest and aerosol in-cloud processing by shallow convective clouds. Based on the similarities among the number densities, the size distributions and the composition of the aerosol in the MBL and the nocturnal residual layer we propose that the air originating in the MBL is transported above the nocturnal mixed layer up to 300-400km inland over the rain forest by night without significant processing

Single particle analysis of the accumulation mode aerosol over the northeast Amazonian tropical rain forest, Surinam, South America

International audienceSingle particle analysis of aerosols particles larger than 0.2 ?m diameter was performed on 24 samples collected over Surinam tropical rain forest and in the adjacent marine boundary layer (MBL) during the LBA-CLAIRE 98 campaign in March 1998. Elemental composition and morphology of 2308 particles was determined using SEM-EDX. The aerosol particles were divided into seven groups according to their chemical composition: organic particles, mineral dust, aged mineral dust, sea salt, aged sea salt, Ca-rich, and biogenic aerosol. However the organic material in aerosol particles cannot be identified directly by SEM-EDX, we present indirect method of detection of organic material using this technique. Samples were further divided with respect to the distinct atmospheric layers present in the tropical troposphere including MBL, continental mixed layer, cloud convective layer, free troposphere and region of deep convection outflow. The organic and mineral dust particles are two major groups observed over the rainforest. In the MBL also sea salt particles represented a large fraction between 15 and 27%. The organic particles control much of the chemical characteristic of the aerosol in the continental tropical troposphere. Their abundance ranged from less than 20% in the MBL to more than 90% in the free troposphere between 4.5- and 12.6-km altitude. During the transport of the air masses from the MBL over the rain forest, fraction of organic aerosol particles more than doubled, reaching 40?60% in the continental boundary layer. This increase was attributed to direct emissions of biogenic aerosols from the tropical vegetation. The high fraction of the organic accumulation mode particles in the upper tropical troposphere could be a good indicator for the air masses originated over the tropical rain forest