ORCID Profile
0000-0002-3220-4177
Current Organisations
Johns Hopkins University
,
University of Oxford
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
Publisher: Springer Science and Business Media LLC
Date: 21-10-2008
Publisher: AIP Publishing
Date: 28-10-2012
DOI: 10.1063/1.4762445
Abstract: By performing a stochastic dynamic in a space of Slater determinants, the full configuration interaction quantum Monte Carlo (FCIQMC) method has been able to obtain energies which are essentially free from systematic error to the basis set correlation energy, within small and systematically improvable error bars. However, the weakly exponential scaling with basis size makes converging the energy with respect to basis set costly and in larger systems, impossible. To ameliorate these basis set issues, here we use perturbation theory to couple the FCIQMC wavefunction to an explicitly correlated strongly orthogonal basis of geminals, following the ${ [2]_{\\textrm {R12}} }$[2]R12 approach of Valeev et al. The required one- and two-particle density matrices are computed on-the-fly during the FCIQMC dynamic, using a s ling procedure which incurs relatively little additional computation expense. The F12 energy corrections are shown to converge rapidly as a function of s ling, both in imaginary time and number of walkers. Our pilot calculations on the binding curve for the carbon dimer, which exhibits strong correlation effects as well as substantial basis set dependence, demonstrate that the accuracy of the FCIQMC-F12 method surpasses that of all previous FCIQMC calculations, and that the F12 correction improves results equivalent to increasing the quality of the one-electron basis by two cardinal numbers.
Publisher: AIP Publishing
Date: 20-12-2017
DOI: 10.1063/1.5008744
Abstract: The rotational spectra of H3N⋯AgI and H2O⋯AgI have been recorded between 6.5 and 18.5 GHz by chirped-pulse Fourier-transform microwave spectroscopy. The complexes were generated through laser vaporisation of a solid target of silver or silver iodide in the presence of an argon gas pulse containing a low concentration of the Lewis base. The gaseous s le subsequently undergoes supersonic expansion which results in cooling of rotational and vibrational motions such that weakly bound complexes can form within the expanding gas jet. Spectroscopic parameters have been determined for eight isotopologues of H3N⋯AgI and six isotopologues of H2O⋯AgI. Rotational constants, B0 centrifugal distortion constants, DJ, DJK or ΔJ, ΔJK and the nuclear quadrupole coupling constants, χaa(I) and χbb(I) − χcc(I) are reported. H3N⋯AgI is shown to adopt a geometry that has C3v symmetry. The geometry of H2O⋯AgI is Cs at equilibrium but with a low barrier to inversion such that the vibrational wavefunction for the v = 0 state has C2v symmetry. Trends in the nuclear quadrupole coupling constant of the iodine nucleus, χaa(I), of L⋯AgI complexes are examined, where L is varied across the series (L = Ar, H3N, H2O, H2S, H3P, or CO). The results of experiments are reported alongside those of ab initio calculations at the CCSD(T)(F12*)/AVXZ level (X = T, Q).
Publisher: Oxford University Press (OUP)
Date: 15-07-2007
DOI: 10.1086/518974
Abstract: In contrast with many other countries, isoniazid preventative therapy is not recommended in clinical care guidelines for human immunodeficiency virus (HIV)-infected persons with latent tuberculosis (TB) in India. Seven hundred fifteen HIV-infected mothers and their infants were prospectively followed up for 1 year after delivery at a public hospital in Pune, India. Women were evaluated for active TB during regular clinic visits, and tuberculin skin tests were performed. World Health Organization definitions for confirmed, probable, and presumed TB were used. Poisson regression was performed to determine correlates of incident TB, and adjusted probabilities of mortality were calculated. Twenty-four of 715 HIV-infected women who were followed up for 480 postpartum person-years developed TB, yielding a TB incidence of 5.0 cases per 100 person-years (95% confidence interval [CI], 3.2-7.4 cases per 100 person-years). Predictors of incident TB included a baseline CD4 cell count 50,000 copies/mL (adjusted IRR, 3.92 95% CI, 1.69-9.11), and a positive tuberculin skin test result (adjusted IRR, 3.08 95% CI, 1.27-7.47). Three (12.5%) of 24 women with TB died, compared with 7 (1.0%) of 691 women without TB (IRR, 12.2 95% CI, 2.03-53.33). Among 23 viable infants with mothers with TB, 2 received a diagnosis of TB. Four infants with mothers with TB died, compared with 28 infants with mothers without TB (IRR, 4.71 95% CI, 1.19-13.57). Women with incident TB and their infants had a 2.2- and 3.4-fold increased probability of death, respectively, compared with women without active TB and their infants, controlling for factors independently associated with mortality (adjusted IRR, 2.2 [95% CI, 0.6-3.8] and 3.4 [95% CI, 1.22-10.59], respectively). Among Indian HIV-infected women, we found a high incidence of postpartum TB and associated postpartum maternal and infant death. Active screening and targeted use of isoniazid preventative therapy among HIV-infected women in India should be considered to prevent postpartum maternal TB and associated mother-to-child morbidity and mortality.
Publisher: Springer Science and Business Media LLC
Date: 15-07-2011
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C7CP04315E
Abstract: The structure and properties of a gas phase complex formed between urea and isocyanic acid are characterised through microwave spectroscopy and ab initio calculations at the CCSD(T)(F12*)/aug-cc-pVTZ level.
Publisher: Wiley
Date: 23-09-2013
DOI: 10.1002/WCMS.1172
Publisher: AIP Publishing
Date: 18-11-2016
DOI: 10.1063/1.4967477
Abstract: Complexes formed between H2S and each of CuI, AgI, and AuI have been isolated and structurally characterised in the gas phase. The H2S⋯MI complexes (where M is the metal atom) are generated through laser vaporisation of a metal rod in the presence of a low concentration of H2S and CF3I in a buffer gas of argon undergoing supersonic expansion. The microwave spectra of six isotopologues of each of H2S⋯CuI, H2S⋯AgI and three isotopologues of H2S⋯AuI have been measured by chirped-pulse Fourier transform microwave spectroscopy. The spectra are interpreted to determine geometries for the complexes and to establish the values of structural parameters. The complexes have Cs symmetry at equilibrium and have a pyramidal configuration about the sulfur atom. The local C2 axis of the hydrogen sulfide molecule intersects the linear axis defined by the three heavy atoms at an angle, ϕ = 75.00(47)° for M = Cu, ϕ = 78.43(76)° for M = Ag, and ϕ = 71.587(13)° for M = Au. The trend in the molecular geometries is consistent with significant relativistic effects in the gold-containing complex. The force constant describing the interaction between the H2S and MI sub-units is determined from the measured centrifugal distortion constant, ΔJ, of each complex. Nuclear quadrupole coupling constants, χaa(M) and χaa(I) (where M denotes the metal atom), are determined for H2S⋯CuI and H2S⋯AuI for the first time.
Publisher: Informa UK Limited
Date: 16-06-2011
DOI: 10.1080/09540121.2011.579948
Abstract: Little is known about birth outcomes for HIV-infected women in India. We examine maternal and neonatal birth outcomes in HIV-infected women within the context of enhanced pre-natal care associated with a randomized clinical trial conducted in Pune, India. Birth outcomes of 212 HIV-infected pregnant women were compared with those of 130 HIV-uninfected pregnant women attending a government tertiary care hospital between 2002 and 2004. These women and children were participating in the Six Week Extended-Dose Nevirapine (SWEN) study. Birth outcomes and maternal morbidity data were collected at delivery. We found no differences between HIV-infected and uninfected pregnant women with respect to the proportion with elevated intrapartum blood pressure, ecl sia, oligohydramnios, intrauterine growth restriction (IUGR), preterm delivery, or caesarean section (p>0.05). HIV-infected women were more likely to have peri-partum fever (3% versus 0%, p=0.04). There were no differences in neonatal parameters such as low birth weight (LBW), infants who were small for gestational age, or those having congenital anomalies (p>0.05). Compared with infants of HIV-infected women enrolled antenatally, infants of HIV-infected women enrolled in the post-partum ward had a higher risk of pre-term delivery (20% versus 8%, p=0.02) and LBW (41% versus 22%, p=0.002). HIV-infected women in this cohort in India were not found to have significant negative birth outcomes. Antenatal care was important as those not having received any antenatal care prior to deliver were at increased risk of having a pre-term delivery or an infant with LBW. Based on these data, regular antenatal care provided to HIV-infected women can reduce risk of adverse birth outcomes for their infants.
Publisher: Springer Science and Business Media LLC
Date: 31-10-2012
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/C9FD90075F
Publisher: Public Library of Science (PLoS)
Date: 2009
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 11-2007
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for David Tew.