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P. Roussel

Publications and source records attributed to P. Roussel.

7 recordsLinked to original sources
arXiv2021

The relativistic 5f electronic structure of delocalized $α$-U and localized $δ$-Pu from the self consistent vertex corrected GW approach and X-ray Emission Spectroscopy

The recently developed self-consistent vertex corrected GW method is used to calculate the 5f electronic structure in delocalized $α$-U and localized $δ$-Pu, each of which is confirmed by the historical experimental approaches of direct and inverse photoemission. Tender X-Ray Emission Spectroscopy (XES), in a novel application to 5f electronic structure, is used to experimentally prove the existence of 5f delocalization in $α$-U.

cond-mat.mtrl-sci↗
arXiv2014

Structural analysis of strained LaVO$_3$ thin films

While structure refinement is routinely achieved for simple bulk materials, the accurate structural determination still poses challenges for thin films due on the one hand to the small amount of material deposited on the thicker substrate and, on the other hand, to the intricate epitaxial relationships that substantially complicate standard X-ray diffraction analysis. Using a combined approach, we analyze the crystal structure of epitaxial LaVO$_3$ thin films grown on (100)-oriented SrTiO$_3$. Transmission electron microscopy study reveals that the thin films are epitaxially grown on SrTiO$_3$ and points to the presence of 90$^{\circ}$ oriented domains. The mapping of the reciprocal space obtained by high resolution X-ray diffraction permits refinement of the lattice parameters. We finally deduce that strain accommodation imposes a monoclinic structure onto the LaVO$_3$ film. The reciprocal space maps are numerically processed and the extracted data computed to refine the atomic positions, which are compared to those obtained using precession electron diffraction tomography. We discuss the obtained results and our methodological approach as a promising thin film structure determination for complex systems.

cond-mat.mtrl-sci↗
arXiv2014

Towards the selection of patients requiring ICD implantation by automatic classification from Holter monitoring indices

The purpose of this study is to optimize the selection of prophylactic cardioverter defibrillator implantation candidates. Currently, the main criterion for implantation is a low Left Ventricular Ejection Fraction (LVEF) whose specificity is relatively poor. We designed two classifiers aimed to predict, from long term ECG recordings (Holter), whether a low-LVEF patient is likely or not to undergo ventricular arrhythmia in the next six months. One classifier is a single hidden layer neural network whose variables are the most relevant features extracted from Holter recordings, and the other classifier has a structure that capitalizes on the physiological decomposition of the arrhythmogenic factors into three disjoint groups: the myocardial substrate, the triggers and the autonomic nervous system (ANS). In this ad hoc network, the features were assigned to each group; one neural network classifier per group was designed and its complexity was optimized. The outputs of the classifiers were fed to a single neuron that provided the required probability estimate. The latter was thresholded for final discrimination A dataset composed of 186 pre-implantation 30-mn Holter recordings of patients equipped with an implantable cardioverter defibrillator (ICD) in primary prevention was used in order to design and test this classifier. 44 out of 186 patients underwent at least one treated ventricular arrhythmia during the six-month follow-up period. Performances of the designed classifier were evaluated using a cross-test strategy that consists in splitting the database into several combinations of a training set and a test set. The average arrhythmia prediction performances of the ad-hoc classifier are NPV = 77% $\pm$ 13% and PPV = 31% $\pm$ 19% (Negative Predictive Value $\pm$ std, Positive Predictive Value $\pm$ std). According to our study, improving prophylactic ICD-implantation candidate selection by automatic classification from ECG features may be possible, but the availability of a sizable dataset appears to be essential to decrease the number of False Negatives.

cs.LG↗
arXiv2013

Search for new resonant states in 10C and 11C and their impact on the cosmological lithium problem

The observed primordial 7Li abundance in metal-poor halo stars is found to be lower than its Big-Bang nucleosynthesis (BBN) calculated value by a factor of approximately three. Some recent works suggested the possibility that this discrepancy originates from missing resonant reactions which would destroy the 7Be, parent of 7Li. The most promising candidate resonances which were found include a possibly missed 1- or 2- narrow state around 15 MeV in the compound nucleus 10C formed by 7Be+3He and a state close to 7.8 MeV in the compound nucleus 11C formed by 7Be+4He. In this work, we studied the high excitation energy region of 10C and the low excitation energy region in 11C via the reactions 10B(3He,t)10C and 11B(3He,t)11C, respectively, at the incident energy of 35 MeV. Our results for 10C do not support 7Be+3He as a possible solution for the 7Li problem. Concerning 11C results, the data show no new resonances in the excitation energy region of interest and this excludes 7Be+4He reaction channel as an explanation for the 7Li deficit.

nucl-ex↗
arXiv2006

Einstein et la mecanique quantique - Quelques reperes, quelques surprises

Even if Einstein brought major contributions as a founder of quantum mechanics, he remained deeply unsatisfied with the bases of this structure he knew to be so efficient for physics. His critics are often known through his numerous controversies wih N. Bohr for a few decades. It has long been suggested that his critics were obsolete and came from an aging man and that it was more a question of philosophy anyway. After J. Bell's contribution however it was claimed that the debate could be closed by an experimental proof, a strange experimental intrusion in philosophy or a strange philosophy. Finally, the experiment being performed, in particular in Orsay with the repeatedly successful experiments of A. Aspect, it was claimed that N. Bohr won. Would the debate be closed? Today and fifty years after his death, it seems that Einstein's critics to quantum mechanics are being regarded differently. Why is it so? Is it due to physics coming back to the debate? It will be attempted to accurately report Einstein's writings on the matter and to find elements of answer to the raised questions.

physics.hist-ph↗
arXiv2000

Structural Phase Transition in the 2D Spin Dimer Compound SrCu2(BO3)2

A displacive, 2nd order structural phase transition at Ts=395 K from space group I`4 2 m below Ts to I 4/m c m above Ts has been discovered in the two-dimensional spin dimer compound SrCu2(BO3)2. The temperature evolution of the structure in both phases has been studied by X-ray diffraction and Raman scattering, supplemented by differential scanning calorimetry and SQUID magnetometry. The implications of this transition and of the observed phonon anomalies in Raman scattering for spin-phonon and interlayer coupling in this quantum spin system will be discussed.

cond-mat.str-el↗