Search results for "Ph. D."
showing 10 items of 180 documents
Le Graphe Génératif Gaussien
2009
International audience; Un nuage de points est plus qu'un ensemble de points isolés. La distribution des points peut être gouvernée par une structure topologique cachée, et du point de vue de la fouille de données, modéliser et extraire cette structure est au moins aussi important que d'estimer la seule densité de probabilité du nuage. Dans cet article, nous proposons un modèle génératif basé sur le graphe de Delaunay d'un ensemble de prototypes représentant le nuage de points, et supposant un bruit gaussien. Nous dérivons un algorithme pour la maximisation de la vraisemblance des paramètres, et nous utilisons le critère BIC pour sélectionner la complexité du modèle. Ce travail a pour objec…
Ravinnetason ja ojituksen vaikutus suokasvillisuuden monimuotoisuuteen ja lajikoostumukseen
2013
Lajistollisessa monimuotoisuudessa on havaittavissa ajallista ja paikallista vaihtelua, joka on jo vuosisatojen ajan innoittanut ekologeja selvittämään lajirikkauden määrittäviä tekijöitä. Muun muassa pinta-alan, elinympäristön heterogeenisyyden, energian ja resurssien saatavuuden sekä erilaisten häiriöiden on havaittu vaikuttavan lajistolliseen monimuotoisuuteen. Osa monimuotoisuuteen vaikuttavista prosesseista on yhä huonosti tunnettuja, ja yksittäisen tekijän vaikutusta voi olla vaikea tulkita, sillä eri tekijät ovat keskenään vuorovaikutuksessa. Tämän tutkimuksen tavoitteena oli selvittää suokasvillisuusyhteisöjen avulla, vaikuttavatko resurssit tai häiriö (1) yhteisön lajimäärään (alfa…
Structure of superheavy nuclei along decay chains of element 115
2014
[Introduction] A recent high-resolution α , X -ray, and γ -ray coincidence-spectroscopy experiment offered the first glimpse of excitation schemes of isotopes along α -decay chains of Z = 115. To understand these observations and to make predictions about shell structure of superheavy nuclei below 288 115, we employ two complementary mean-field models: the self-consistent Skyrme energy density functional approach and the macroscopic-microscopic Nilsson model. We discuss the spectroscopic information carried by the new data. In particular, candidates for the experimentally observed E 1 transitions in 276 Mt are proposed. We find that the presence and nature of low-energy E 1 transitions in w…
Different sample treatment approaches for the analysis of T-2 and HT-2 toxins from oats-based media.
2010
A LC-DAD method is proposed for the determination of the T-2 and HT-2 toxins in cultures of Fusarium langsethiae in oat-based and other in vitro media. Test media consisted of freshly prepared milled oats to which T-2 and HT-2 toxin stock solutions were added. Different mixtures of extraction solvent (acetonitrile:water and methanol water), extraction times (30', 60' or 90') and drying methods were investigated. Results showed that extraction with methanol: water (80:20, v/v) for 90 min, drying with N-2 and subsequent analysis by LC-DAD was the fastest and most user friendly method for detecting HT-2 and T-2 toxins production by F. langsethiae strains grown on oat-based media at levels of 0…
Quantum-state-selective decay spectroscopy of 213Ra
2017
An experimental scheme combining the mass resolving power of a Penning trap with contemporary decay spectroscopy has been established at GSI Darmstadt. The Universal Linear Accelerator (UNILAC) at GSI Darmstadt provided a 48Ca beam impinging on a thin 170Er target foil. Subsequent to velocity filtering of reaction products in the Separator for Heavy Ion reaction Products (SHIP), the nuclear ground state of the 5n evaporation channel 213Ra was mass-selected in SHIPTRAP, and the 213Ra ions were finally transferred into an array of silicon strip detectors surrounded by large composite germanium detectors. Based on comprehensive geant4 simulations and supported by theoretical calculations, the …
117番元素Ts合成のための48Ca+249Bk融合反応
2019
We have performed an experiment to synthesize the element 117 (Ts) with the $^{48}$Ca+$^{249}$Bk fusion reaction. Four $\alpha$-decay chains attributed to the element 117 were observed. Two of them were long decay chains which can be assigned to the one originating from the $\alpha$ decay of $^{294}$Ts. The other two were short decay chains which are consistent with the one originating from the $\alpha$ decay of $^{293}$Ts. We have compared the present results with the literature data, and found that our present results mostly confirmed the literature data, leading to the firm confirmation of the synthesis of the element 117.
Graph
2020
A graph is any abstract object that consists of vertices and edges. This entry presents the main attributes of vertices and edges.
Laser assisted decay spectroscopy at the CRIS beam line at ISOLDE
2012
A new collinear resonant ionization spectroscopy (Cris)beam line has recently been installed at Isolde, Cern utilising lasers to combine collinear laser spectroscopy and resonant ionization spectroscopy. The combined technique offers the ability to purify an ion beam that is heavily contaminated with radioactive isobars, including the ground state of an isotope from its isomer, allowing sensitive secondary experiments to be performed. A new programme aiming to use the Cris technique for the separation of nuclear isomeric states for decay spectroscopy will commence in 2011. A decay spectroscopy station, consisting of a rotating wheel implantation system for alpha decay spectroscopy, and thre…
In-beam spectroscopic study of $^{244}$Cf
2018
The ground-state rotational band of the neutron-deficient californium ( Z = 98 ) isotope 244 Cf was identified for the first time and measured up to a tentative spin and parity of I π = 20 + . The observation of the rotational band indicates that the nucleus is deformed. The kinematic and dynamic moments of inertia were deduced from the measured γ -ray transition energies. The behavior of the dynamic moment of inertia revealed an up-bend due to a possible alignment of coupled nucleons in high- j orbitals starting at a rotational frequency of about ℏ ω = 0.20 MeV . The results were compared with the systematic behavior of the even-even N = 146 isotones as well as with available theoretical c…
Decay studies of the long-lived states in Tl186
2020
Decay spectroscopy of the long-lived states in 186Tl has been performed at the ISOLDE Decay Station at ISOLDE, CERN. The α decay from the low-spin (2−) state in 186Tl was observed for the first time and a half-life of 3.4+0.5−0.4 s was determined. Based on the α-decay energy, the relative positions of the long-lived states were fixed, with the (2−) state as the ground state, the 7(+) state at 77(56) keV, and the 10(−) state at 451(56) keV. The level scheme of the internal decay of the 186Tl(10(−)) state [T1/2=3.40(9) s], which was known to decay solely through emission of 374-keV γ-ray transition, was extended and a lower limit for the β-decay branching bβ>5.9(3)% was determined. The extrac…