Atomic spectral-product representations of molecular electronic structure: metric matrices and atomic-product composition of molecular eigenfunctions

Recent progress is reported in development of ab initio computational methods for the electronic structures of molecules employing the many-electron eigenstates of constituent atoms in spectral-product forms. The approach provides a universal atomic-product description of the electronic structure of matter as an alternative to more commonly employed valence-bond- or molecular-orbital-based representations. The Hamiltonian matrix in this representation is seen to comprise a sum over atomic energies and a pairwise sum over Coulombic interaction terms that depend only on the separations of the individual atomic pairs. Overall electron antisymmetry can be enforced by unitary transformation when appropriate, rather than as a possibly encumbering or unnecessary global constraint. The matrix representative of the antisymmetrizer in the spectral-product basis, which is equivalent to the metric matrix of the corresponding explicitly antisymmetric basis, provides the required transformation to antisymmetric or linearly independent states after Hamiltonian evaluation. Particular attention is focused in the present report on properties of the metric matrix and on the atomic-product compositions of molecular eigenstates as described in the spectral-product representations. Illustrative calculations are reported for simple but prototypically important diatomic (H_2, CH) and triatomic (H_3, CH_2) molecules employing algorithms and computer codes devised recently for this purpose. This particular implementation of the approach combines Slater-orbital-based one- and two-electron integral evaluations, valence-bond constructions of standard tableau functions and matrices, and transformations to atomic eigenstate-product representations. The calculated metric matrices and corresponding potential energy surfaces obtained in this way elucidate a number of aspects of the spectral-product development, including the nature of closure in the representation, the general redundancy or linear dependence of its explicitly antisymmetrized form, the convergence of the apparently disparate atomic-product and explicitly antisymmetrized atomic-product forms to a common invariant subspace, and the nature of a chemical bonding descriptor provided by the atomic-product compositions of molecular eigenstates. Concluding remarks indicate additional studies in progress and the prognosis for performing atomic spectral-product calculations more generally and efficiently

Most CD4+ T cells from human immunodeficiency virus-1 infected patients can undergo prolonged clonal expansion

We have addressed the capacity of HIV-1 infection to alter the growth of primary CD4+ T cells, but at the clonal level. Single T cells were expanded in the presence of PHA, IL-2, and small numbers of accessory dendritic cells. We report two new findings. First, T cells from seropositive individuals, even those with AIDS and markedly reduced CD4+ counts, exhibit a normal cloning efficiency, and proliferative capacity. This result is in contrast to two prior reports of a low cloning efficiency in CD4+ T cells from HIV-1-infected patients. Second, when we added high doses of exogenous HIV-1 to T cell clones from control subjects, we observed infection but not cytotoxity or loss of CD4+ cells, following addition of virus stocks at days 0, 3, and/or 7 of clonal growth. The same HIV-1 isolates markedly reduced CD4+ T cells in bulk mononuclear cultures. When tested at day 11, HIV-1 mRNA was expressed in some cells of exogenously infected clones by in situ hybridization; when tested at day 18, several clones could transactivate a TAT-sensitive cell line. These findings suggest that the loss of CD4+ T cells in infected individuals is not the inevitable result of the activation of latent infection, or spread of a productive infection, during clonal growth

Boost-phase discrimination research

The final report describes the combined work of the Computational Chemistry and Aerothermodynamics branches within the Thermosciences Division at NASA Ames Research Center directed at understanding the signatures of shock-heated air. Considerable progress was made in determining accurate transition probabilities for the important band systems of NO that account for much of the emission in the ultraviolet region. Research carried out under this project showed that in order to reproduce the observed radiation from the bow shock region of missiles in their boost phase it is necessary to include the Burnett terms in the constituent equation, account for the non-Boltzmann energy distribution, correctly model the NO formation and rotational excitation process, and use accurate transition probabilities for the NO band systems. This work resulted in significant improvements in the computer code NEQAIR that models both the radiation and fluid dynamics in the shock region

Placenta accreta:adherent placenta due to Asherman syndrome

It is important to be aware of the risk of abnormally invasive placenta in patients with a history of Asherman syndrome and uterine scarring. A prenatal diagnosis by ultrasonography is useful when planning of mode of delivery

Benchmark full configuration-interaction calculations on HF and NH2

Full configuration-interaction (FCI) calculations are performed at selected geometries for the 1-sigma(+) state of HF and the 2-B(1) and 2-A(1) states of NH2 using both DZ and DZP gaussian basis sets. Higher excitations become more important when the bonds are stretched and the self-consistent field (SCF) reference becomes a poorer zeroth-order description of the wave function. The complete active space SCF - multireference configuration-interaction (CASSCF-MRCI) procedure gives excellent agreement with the FCI potentials, especially when corrected with a multi-reference analog of the Davidson correction

Prevalence and main outcomes of placenta accreta spectrum: a systematic review and metaanalysis

OBJECTIVE: The objective of this study was to evaluate the prevalence of placenta accreta spectrum in general population studies and the main maternal outcomes at delivery. STUDY DESIGN: Data sources: We searched PubMed, Google Scholar, clinicalTrials.gov and MEDLINE between 1982 and 2018. STUDY ELIGIBILITY CRITERIA: Articles providing data on the number of cases of placenta accreta spectrum per pregnancies, births or deliveries in a defined population. STUDY APPRAISAL AND SYNTHESIS METHODS: Study characteristics were evaluated by two independent reviewers using a predesigned protocol. Primary outcomes were the prevalence of placenta accreta spectrum and clinical diagnostic at birth and pathologic criteria used to confirm the diagnosis. Secondary outcomes included cases requiring transfusion, incidence of peripartum hysterectomy and maternal mortality rates. Heterogeneity between studies was analysed with the Cochran's Q-test and the I2 statistics. RESULTS: Of the 98 full-text studies identified, 29 articles met the defined criteria including 22 retrospective and 7 prospective studies comprising 7,001 cases of placenta accreta spectrum out 5,719,992 births. Prevalence rates ranged between 0.01 and 0.1% with an overall pooled prevalence of 0.17% (95% CI 0.14-0.19). Only 10 studies provided with detailed histopathologic data. The pool prevalence for the adherent versus the invasive grades was 0.5 (95% CI 0.3-0.36) and 0.3 (95% CI 0.2-0.4) per 1000 births, respectively. The pooled incidence for peripartum hysterectomy was 52.2% (95% CI 38.3-66.4; I2= 99.8%) and 46.9% (95 % CI 34-59.9, I2= 98.8%) for haemorrhage requiring transfusion. The pooled estimate of maternal death was 0.05% (95% CI 0.06-0.69, I2=73%). We found large amounts of heterogeneity between studies for all parameters and further quantifying was limited because of methodological inconsistencies between studies with regards to clinical criteria used for the diagnosis of the condition at birth and the histopathologic confirmation of the diagnosis and differential diagnosis between adherent and invasive accreta placentation. CONCLUSIONS: This meta-analysis indicates wide variation between studies for the prevalence rate of placenta accreta spectrum and for the different grades of accreta placentation, highlighting the need for consistency in definitions used to describe placenta accreta spectrum at birth and in reporting on this increasing common obstetric complication

Epidemiology of placenta previa accreta: a systematic review and meta-analysis

Objective To estimate the prevalence and incidence of placenta previa complicated by placenta accreta spectrum (PAS) and to examine the different criteria being used for the diagnosis. Design Systematic review and meta-analysis. Data sources PubMed, Google Scholar, ClinicalTrials.gov and MEDLINE were searched between August 1982 and September 2018. Eligibility criteria Studies reporting on placenta previa complicated by PAS diagnosed in a defined obstetric population. Data extraction and synthesis Two independent reviewers performed the data extraction using a predefined protocol and assessed the risk of bias using the Newcastle-Ottawa scale for observational studies, with difference agreed by consensus. The primary outcomes were overall prevalence of placenta previa, incidence of PAS according to the type of placenta previa and the reported clinical outcomes, including the number of peripartum hysterectomies and direct maternal mortality. The secondary outcomes included the criteria used for the prenatal ultrasound diagnosis of placenta previa and the criteria used to diagnose and grade PAS at birth. Results A total of 258 articles were reviewed and 13 retrospective and 7 prospective studies were included in the analysis, which reported on 587 women with placenta previa and PAS. The meta-analysis indicated a significant (p<0.001) heterogeneity between study estimates for the prevalence of placenta previa, the prevalence of placenta previa with PAS and the incidence of PAS in the placenta previa cohort. The median prevalence of placenta previa was 0.56% (IQR 0.39–1.24) whereas the median prevalence of placenta previa with PAS was 0.07% (IQR 0.05–0.16). The incidence of PAS in women with a placenta previa was 11.10% (IQR 7.65–17.35). Conclusions The high heterogeneity in qualitative and diagnostic data between studies emphasises the need to implement standardised protocols for the diagnoses of both placenta previa and PAS, including the type of placenta previa and grade of villous invasiveness. PROSPERO registration number CRD4201706858

Recent advances in electronic structure theory and their influence on the accuracy of ab initio potential energy surfaces

Recent advances in electronic structure theory and the availability of high speed vector processors have substantially increased the accuracy of ab initio potential energy surfaces. The recently developed atomic natural orbital approach for basis set contraction has reduced both the basis set incompleteness and superposition errors in molecular calculations. Furthermore, full CI calculations can often be used to calibrate a CASSCF/MRCI approach that quantitatively accounts for the valence correlation energy. These computational advances also provide a vehicle for systematically improving the calculations and for estimating the residual error in the calculations. Calculations on selected diatomic and triatomic systems will be used to illustrate the accuracy that currently can be achieved for molecular systems. In particular, the F+H2 yields HF+H potential energy hypersurface is used to illustrate the impact of these computational advances on the calculation of potential energy surfaces

Nondipole Resonant X-ray-Raman Spectroscopy: Polarized Inelastic Scattering at the K Edge of Cl2

Experimental and theoretical studies are reported on the inelastic (Raman) scattering of wavelength-selected polarized x rays from the K edge of gas-phase chlorine molecules. The polarized emission spectra exhibit prominent nondipole features consequent of phase variations of the incident and emitted radiation over molecular dimensions, as predicted by the Kramers-Heisenberg scattering formalism. Issues pursuant to the detection of core-hole localization by resonant Raman scattering from homonuclear diatomic molecules are critically examined. [S0031-9007(97)03486-8