Triple Test Screening for Down Syndrome: Looking Back on a False-Positive Result and Having or Not Having a Triple Test in Subsequent Pregnancies

Objectives: It was the main aim of the present retrospective study carried out in Flanders to evaluate how women with a false-positive triple test result look back on their experience and decision making and how many of them make use of the triple test in subsequent pregnancies. Methods: All 508 women tested in the Centre for Human Genetics in Leuven in 1995 who had a positive triple test result followed by a normal amniocentesis outcome were invited to participate in a mailed questionnaire study with open and multiple choice questions in 1998. The response rate was 68%. Results: The answers to the multiple choice question assessing how they look back on their initial expectations regarding the exact meaning of the triple test revealed that less than one half reported that it concerned the identification of 'a higher risk of carrying a child with Down syndrome (DS)'. Reporting correct initial expectations was significantly associated with a higher education level. The same holds for indecisiveness regarding pregnancy termination should the amniocentesis have detected a fetus with DS. As expected, a large majority of the women reported a high level of distress or worry after the communication of the positive triple test result. Overall the findings show that retrospectively most women had the feeling that the decision to have amniocentesis was their own decision rather than a professional's. Of the subgroup with one or more subsequent pregnancies 70% had another triple test. Conclusions: The overall results of this study clearly reveal a need for a systematic approach aimed at better informing and counselling pregnant women about the implications and limitations of the triple test. Notwithstanding the reported high level of distress caused by a positive triple test result, a large majority of the women with subsequent pregnancies had another triple test; they represent a clearly higher percentage than in another recent study. Copyright 2001 S. Karger AG, Basel     

Green's function study of the one-electron and shake-up ionization spectra of unsaturated hydrocarbon cage compounds

The valence one-electron and shake-up ionization spectra of stella-2,6-diene, stella-2,6-dione, bicyclo-[2.2.2]-octane-2,5-dione, and bicyclo-[2.2.1]-heptane-2,5-dione have been exhaustively studied, up to the double ionization threshold and beyond, by means of one-particle Green's function theory. This study is based on calculations employing the outer-valence Green's function and the third-order algebraic diagrammatic construction schemes, along with a variety of basis sets. A comparison is made with available ultraviolet (He I) photoelectron and (e, 2e) electron-impact ionization spectra, with main focus on the identification of spectral fingerprints for cyclic strains and through-bond pi-conjugation. As a byproduct, our results demonstrate that it is impossible to reliably assign complex (e, 2e) ionization spectra by resorting only to Hartree-Fock or Kohn-Sham orbital energies and to the related electron momentum distributions.     

Spin-flip processes and ultrafast magnetization dynamics in Co: Unifying the microscopic and macroscopic view of femtosecond magnetism

The femtosecond magnetization dynamics of a thin cobalt film excited with ultrashort laser pulses has been studied using two complementary pump-probe techniques, namely, spin-, energy-, and time-resolved photoemission and the time-resolved magneto-optical Kerr effect. Combining the two methods, it is possible to identify the microscopic electron spin-flip mechanisms responsible for the ultrafast macroscopic magnetization dynamics of the cobalt film. In particular, we show that electron-magnon excitation does not affect the overall magnetization even though it is an efficient spin-flip channel on the sub-200 fs time scale. Instead, we find experimental evidence for the relevance of Elliott-Yafet-type spin-flip processes for the ultrafast demagnetization taking place on a time scale of 300 fs.     

Probing the transition in bulk Ce under pressure: a direct investigation by resonant inelastic X-ray scattering

We report on the most complete investigation to date of the -electron properties at the transition in elemental Ce by resonant inelastic x-ray scattering (RIXS). The Ce 2p3d-RIXS spectra were measured directly in the bulk material as a function of pressure through the transition. The spectra were simulated within the Anderson impurity model. The occupation number n(f) and f double occupancy were derived from the calculations in both gamma and alpha phases in the ground state. We find that the electronic structure changes result mainly from band formation of 4f electrons which concurs with reduced electron correlation and increased Kondo screening at high pressure.     

Co-doped (La, Sr)TiO(3-delta) : a high Curie temperature diluted magnetic system with large spin polarization

We report on tunneling magnetoresistance (TMR) experiments that demonstrate the existence of a significant spin polarization in Co-doped (La, Sr)TiO(3-delta) (Co-LSTO), a ferromagnetic diluted magnetic oxide system (DMOS) with high Curie temperature. These TMR experiments have been performed on magnetic tunnel junctions associating Co-LSTO and Co electrodes. Extensive structural analysis of Co-LSTO combining high-resolution transmission electron microscopy and Auger electron spectroscopy excluded the presence of Co clusters in the Co-LSTO layer and thus, the measured ferromagnetism and high spin polarization are intrinsic properties of this DMOS. Our results argue for the DMOS approach with complex oxide materials in spintronics.     

Parity-violating electron scattering from 4He and the strange electric form factor of the nucleon

We have measured the parity-violating electroweak asymmetry in the elastic scattering of polarized electrons from 4He at an average scattering angle = 5.7 degrees and a four-momentum transfer Q2 = 0.091 GeV2 . From these data, for the first time, the strange electric form factor of the nucleon G(E)s can be isolated. The measured asymmetry of A(PV) = (6.72 +/- 0.84(stat) +/- 0.21(syst) x 10(-6) yields a value of G(E)s = -0.038 +/- 0.042(stat) +/- 0.010(syst), consistent with zero.     

Importance of backdonation in [M-(CO)]p+ complexes isoelectronic to [Au-(CO)]+

In this contribution, we study several monocarbonyl-metal complexes in order to unravel the contribution of relativistic effects to the metal-ligand bond length and complexation energy. Using scalar density functional theory (DFT) constrained space orbital variation (CSOV) energy decomposition analysis supplemented by all-electron four-component DFT computations, we describe the dependency of relativistic effects on the orbitals involved in the complexation for the Au(+) isoelectronic series, namely, the fully occupied 5d orbitals and the empty 6s orbitals. We retrieve the well-known sensitivity of gold toward relativity. For platinum and gold, the four-component results illustrate the simultaneous relativistic expansion of the 5d orbitals and the contraction of the 6s orbitals. The consequences of such modifications are evidenced by CSOV computations, which show the importance of both donation and backdonation within such complexes. This peculiar synergy fades away with mercury and thallium for which coordination becomes driven by the accepting 6s orbitals only, which makes the corresponding complexes less sensitive toward the relativistic effects.     

Synthése d'époxydes et d'éthers glycidiques á chaîne chlorofluorée

Epoxides of general formula

(II, V) (R_F,Cl = Cl ; CF₃ ; Cl(CFClCF₂)_n?) are prepared from chlorohydrines R_F,ClCCl₂CH₂CHClCH₂OH (I).These chlorhydrines are monoadducts of carbon tetrachloride 1,1,1 trichlorotrifluoroethane, telomers Cl(CFClCF₂)_nCCl₃, with allyl alcohol.Reactions of these epoxides with lithium aluminium hydride and/or sulfuric acid lead to corresponding secondary alcohols and/or diols. Glycidyl ethers of (I) and (II,n) with epichlorhydrin could not be obtained. However, epichlorhydrin reacts with the more acidic chlorofluorinated alcohol CFCl₂CF₂CH₂OH. Thus, the glycidyl ether

is prepared.     

Norbornane: an investigation into its valence electronic structure using electron momentum spectroscopy, and density functional and Green's function theories

We report on the results of an exhaustive study of the valence electronic structure of norbornane (C(7)H(12)), up to binding energies of 29 eV. Experimental electron momentum spectroscopy and theoretical Green's function and density functional theory approaches were all utilized in this investigation. A stringent comparison between the electron momentum spectroscopy and theoretical orbital momentum distributions found that, among all the tested models, the combination of the Becke-Perdew functional and a polarized valence basis set of triple-zeta quality provides the best representation of the electron momentum distributions for all of the 20 valence orbitals of norbornane. This experimentally validated quantum chemistry model was then used to extract some chemically important properties of norbornane. When these calculated properties are compared to corresponding results from other independent measurements, generally good agreement is found. Green's function calculations with the aid of the third-order algebraic diagrammatic construction scheme indicate that the orbital picture of ionization breaks down at binding energies larger than 22.5 eV. Despite this complication, they enable insights within 0.2 eV accuracy into the available ultraviolet photoemission and newly presented (e,2e) ionization spectra, except for the band associated with the 1a(2) (-1) one-hole state, which is probably subject to rather significant vibronic coupling effects, and a band at approximately 25 eV characterized by a momentum distribution of "s-type" symmetry, which Green's function calculations fail to reproduce. We note the vicinity of the vertical double ionization threshold at approximately 26 eV.     

Diastereoselective hydroxylation of 6-substituted piperidin-2-ones. An efficient synthesis of (2S,5R)-5-hydroxylysine and related alpha-amino acids

The synthesis of (2S,5R)-5-hydroxy-6-oxo-1,2-piperidinedicarboxylates (5) and related (3S,6R)-3-hydroxy-6-alkyl-2-oxo-1-piperidinecarboxylates has been developed. The approach is based on the asymmetric hydroxylation of enolates generated from the corresponding N-protected-6-substituted piperidin-2-ones. The utility of 5a as a precursor in the synthesis of (2S,5R)-5-hydroxylysine (1), an amino acid unique to collagen and collagen-like proteins, has also been demonstrated. (2S)-6-oxo-1,2-piperidinedicarboxylates (6) required for hydroxylation studies were prepared in 38-74% yield, starting from conveniently protected aspartic acid as inexpensive chiral adduct. Hydroxylation of 6 to 5 proceeds in high yield and excellent diastereoselectivity by treatment of their Li-enolate with (+)-camphorsulfonyloxaziridine at -78 degrees C. Ring opening of di-tert-butyl (2S,5R)-6-oxo-1,2-piperidinedicarboxylate ((5R)-5a) under reductive conditions afforded the corresponding 1,2-diol (17) in 91%, which was further transformed to (2S,5R)-5-hydroxylysine in four steps (84%). 17 is also a versatile intermediate in the preparation of tert-butyl (2S,5R)-2-[(tert-butoxycarbonyl)amino]-5-hydroxy-6-iodohexanoate (3) and tert-butyl (2S)-2-[(tert-butoxycarbonyl)amino]-4-[(2R)-oxiranyl]butanoate (4), two amino acid derivatives used in the total synthesis of the bone collagen cross-link (+)-pyridinoline (2a).