Polarization in Strong-Field Ionization of Excited Helium

We analyze how bound-state excitation, electron exchange and the residual binding potential influence above-threshold ionization (ATI) in helium prepared in an excited p state, oriented parallel and perpendicular to a linearly polarized mid-IR field. Using the ab initio B-spline algebraic diagrammatic construction, and several one-electron methods with effective potentials, including the Schrödinger solver Qprop, modified versions of the strong-field approximation (SFA) and the Coulomb quantum-orbit strong-field approximation, we find that these specific physical mechanisms leave significant imprints in ATI spectra and photoelectron momentum distributions. Examples are changes of up to two orders of magnitude in the high-energy photoelectron region, and ramp-like structures that can be traced back to Coulomb-distorted trajectories. The present work also shows that electron exchange renders rescattering less effective, causing suppressions in the ATI plateau. Due to the long-range potential, the electron continuum dynamics are no longer confined to the polarization axis, in contrast to the predictions of traditional approaches. Thus, one may in principle probe excited-state configurations perpendicular to the driving-field polarization without the need for orthogonally polarized fields

Association Between Assisted Reproductive Technology Conception and Autism in California, 1997–2007

Objectives. We assessed the association between assisted reproductive technology (ART) and diagnosed autistic disorder in a population-based sample of California births. Methods. We performed an observational cohort study using linked records from the California Birth Master Files for 1997 through 2007, the California Department of Developmental Services autism caseload for 1997 through 2011, and the Centers for Disease Control and Prevention’s National ART Surveillance System for live births in 1997 through 2007. Participants were all 5 926 251 live births, including 48 865 ART-originated infants and 32 922 cases of autism diagnosed by the Department of Developmental Services. We compared births originated using ART with births originated without ART for incidence of autism.Results. In the full population, the incidence of diagnosed autism was twice as high for ART as non-ART births. The association was diminished by excluding mothers unlikely to use ART; adjustment for demographic and adverse prenatal and perinatal outcomes reduced the association substantially, although statistical significance persisted for mothers aged 20 to 34 years. Conclusions. The association between ART and autism is primarily explained by adverse prenatal and perinatal outcomes and multiple births

Does Autism Diagnosis Age or Symptom Severity Differ Among Children According to Whether Assisted Reproductive Technology was Used to Achieve Pregnancy?

Previous studies report associations between conception with assisted reproductive technology (ART) and autism. Whether these associations reflect an ascertainment or biologic effect is undetermined. We assessed diagnosis age and initial autism symptom severity among[30,000 children with autism from a linkage study of California Department of Developmental Services records, birth records, and the National ART Surveillance System. Median diagnosis age and symptom severity levels were significantly lower for ART-conceived than non-ART- conceived children. After adjustment for differences in the socio-demographic profiles of the two groups, the diagno- sis age differentials were greatly attenuated and there were no differences in autism symptomatology. Thus, ascer- tainment issues related to SES, not ART per se, are likely the driving influence of the differences we initially observed