51 research outputs found
Early Atomic Models - From Mechanical to Quantum (1904-1913)
A complete history of early atomic models would fill volumes, but a
reasonably coherent tale of the path from mechanical atoms to the quantum can
be told by focusing on the relevant work of three great contributors to atomic
physics, in the critically important years between 1904 and 1913: J. J.
Thomson, Ernest Rutherford and Niels Bohr. We first examine the origins of
Thomson's mechanical atomic models, from his ethereal vortex atoms in the early
1880's, to the myriad "corpuscular" atoms he proposed following the discovery
of the electron in 1897. Beyond predictions for the periodicity of the
elements, the application of Thomson's atoms to problems in scattering and
absorption led to quantitative predictions that were confirmed by experiments
with high-velocity electrons traversing thin sheets of metal. Still, the much
more massive and energetic {\alpha}-particles being studied by Rutherford were
better suited for exploring the interior of the atom, and careful measurements
on the angular dependence of their scattering eventually allowed him to infer
the existence of an atomic nucleus. Niels Bohr was particularly troubled by the
radiative instability inherent to any mechanical atom, and succeeded in 1913
where others had failed in the prediction of emission spectra, by making two
bold hypotheses that were in contradiction to the laws of classical physics,
but necessary in order to account for experimental facts.Comment: 58 Pages + References, 8 Figures. Accepted for publication in the
European Physical Journal H (Historical Perspectives on Contemporary
Physics). V2 - minor typos corrected and a footnote added to p.2
Genetic associations at 53 loci highlight cell types and biological pathways relevant for kidney function.
Reduced glomerular filtration rate defines chronic kidney disease and is associated with cardiovascular and all-cause mortality. We conducted a meta-analysis of genome-wide association studies for estimated glomerular filtration rate (eGFR), combining data across 133,413 individuals with replication in up to 42,166 individuals. We identify 24 new and confirm 29 previously identified loci. Of these 53 loci, 19 associate with eGFR among individuals with diabetes. Using bioinformatics, we show that identified genes at eGFR loci are enriched for expression in kidney tissues and in pathways relevant for kidney development and transmembrane transporter activity, kidney structure, and regulation of glucose metabolism. Chromatin state mapping and DNase I hypersensitivity analyses across adult tissues demonstrate preferential mapping of associated variants to regulatory regions in kidney but not extra-renal tissues. These findings suggest that genetic determinants of eGFR are mediated largely through direct effects within the kidney and highlight important cell types and biological pathways
Sur l'ionisation de différents gaz par les particules α du radium
Pas de Résumé disponibl
La nature des rayons γ et des rayons X
Pas de Résumé disponibl
Les particules α de l'uranium et du thorium
Pas de Résumé disponibl
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