60 research outputs found
An Optical Lattice Clock with Spin-polarized 87Sr Atoms
We present a new evaluation of an 87Sr optical lattice clock using spin
polarized atoms. The frequency of the 1S0-3P0 clock transition is found to be
429 228 004 229 873.6 Hz with a fractional accuracy of 2.6 10^{-15}, a value
that is comparable to the frequency difference between the various primary
standards throughout the world. This measurement is in excellent agreement with
a previous one of similar accuracy
Directed Synthesis of Crystalline Plutonium(III) and (IV) Oxalates: Accessing Redox-Controlled Separations in Acidic Solutions
Chemo-enzymatic synthesis of a series of 2,4-syn-functionalized (S)-glutamate analogues: new insight into the structure-activity relation of ionotropic glutamate receptor subtypes 5, 6, and 7.
International audience(S)-Glutamic acid (Glu) is the major excitatory neurotransmitter in the central nervous system (CNS) activating the plethora of ionotropic Glu receptors (iGluRs) and metabotropic Glu receptors (mGluRs). In this paper, we present a chemo-enzymatic strategy for the enantioselective synthesis of five new Glu analogues 2aâf (2d is exempt) holding a functionalized substituent in the 4-position. Nine Glu analogues 2aâj are characterized pharmacologically at native 2-amino-3-(3-hydroxy-5-methyl-4-isoxazolyl)propionic acid (AMPA), kainic acid (KA), and N-methyl-D-aspartic acid (NMDA) receptors in rat synaptosomes as well as in binding assays at cloned rat iGluR5â7 subtypes. A detailed in silico study address as to why 2h is a high-affinity ligand at iGluR5â7 (Ki = 3.81, 123, 57.3 nM, respectively), while 2e is only a high affinity ligand at iGluR5 (Ki = 42.8 nM). Furthermore, a small series of commercially available iGluR ligands are characterized in iGluR5â7 bindin
Evaluating and Minimizing Distributed Cavity Phase Errors in Atomic Clocks
We perform 3D finite element calculations of the fields in microwave cavities
and analyze the distributed cavity phase errors of atomic clocks that they
produce. The fields of cylindrical cavities are treated as an azimuthal Fourier
series. Each of the lowest components produces clock errors with unique
characteristics that must be assessed to establish a clock's accuracy. We
describe the errors and how to evaluate them. We prove that sharp structures in
the cavity do not produce large frequency errors, even at moderately high
powers, provided the atomic density varies slowly. We model the amplitude and
phase imbalances of the feeds. For larger couplings, these can lead to
increased phase errors. We show that phase imbalances produce a novel
distributed cavity phase error that depends on the cavity detuning. We also
design improved cavities by optimizing the geometry and tuning the mode
spectrum so that there are negligible phase variations, allowing this source of
systematic error to be dramatically reduced.Comment: To appear in Metrologi
Low incidence of SARS-CoV-2, risk factors of mortality and the course of illness in the French national cohort of dialysis patients
Oxydes d'actinides à façon pour la fabrication de combustibles nucléaires de Génération IV
International audienceCette Ă©tude sâinscrit dans le cadre des recherches menĂ©es sur le traitement-recyclage descombustibles nuclĂ©aires du futur et, plus prĂ©cisĂ©ment, sur la fabrication de nouveaux combustiblessous forme de pastilles Ă partir de poudres dâoxydes Ă base dâactinides de diffĂ©rentesmorphologies. DiffĂ©rents procĂ©dĂ©s de conversion sont envisagĂ©s pour la synthĂšse dâoxydesdâactinides Ă partir de lâuranium et du plutonium issus du traitement des combustibles usĂ©s.Plusieurs Ă©tudes menĂ©es au CEA sur le procĂ©dĂ© de conversion par voie oxalique ont permisdâaboutir Ă des oxalates et Ă des oxydes dâactinides de morphologies trĂšs variĂ©es en fonction desparamĂštres de prĂ©cipitation
" UIV/LnIII unexpected mixed site in polymetallic oxalato complexes. Part II. Substitution of UIV for LnIII in the new oxalates (N2H5)Ln(C2O4)2.nH2O (Ln = Nd, Gd)."
"U(IV)/Ln(III) unexpected mixed site in polymetallic oxalato complexes. Part I. Substitution of Ln(III) for U(IV) from the new oxalate (NH4)2U2(C2O4)5. 2.5H2O."
" Crystal Structure of New Uranyl Oxalates (NH4)2[UO2(C2O4)2.H2O].2H2O and (NH4)2-x(N2H5)x (UO2)2(C2O4)3.3H2O (x 0 and x = 1). Comparison with other Uranyl Oxalates."
- âŠ