135,871 research outputs found
View from the bridge: a pseudo-Jahn-Teller approach to transition metal hydrosilane complexes
No full textThe model complex [Cp(CO)(2)Mn(SiH4)] has been studied by time-dependent DFT methods: hence, it is shown to be unstable with respect to a pseudo-Jahn-Teller distortion which brings an equatorial Si-H moiety into contact with the Mn centre.</p
Examination of the Jahn-Teller physics of NaNi02 and LiNi02 using x-ray absorption spectroscopy and configuration interaction
No full text This thesis examines available x-ray absorption spectroscopy (XAS) data for NiO, NaNi02 , and LiNi02 . The XAS examined is the Ni L-edge, 3d^n2p^6 →t 3d^(n+1)2p^5 . The experimental spectra are compared to spectra calculated using a configuration interaction approach. This approach reproduces the spectra accurately. The NaNi02 spectrum is shown to be sensitive to the Jahn-Teller distortion, while the LiNi02 spectrum is reproduced by a hybridized d^7-d^8 state that explains the lack of Jahn-Teller distortion in LiNi02 ThesisMaster of Science (MSc
Estimating the need for antiretroviral treatment and an assessment of a simplified HIV/AIDS case definition in rural Malawi.
No full textBACKGROUND: Surveillance in the era of antiretroviral therapy (ART) requires estimates of HIV prevalence as well as the proportion eligible for ART. We estimated HIV prevalence and assessed field staging of individuals to estimate the burden of HIV disease needing treatment in rural Malawi. METHODS: Adults aged 18-59 years in a demographic surveillance system were interviewed, examined, and HIV counselled and tested. Staging that used a simplified version of the WHO criteria ('field checklist') was compared with staging by a medical assistant using a 'clinic checklist' and to CD4 cell results. RESULTS: A total of 2129 of 2303 eligible adults (92.4%) were traced, and 2047 (96.1%) participated. Of the 1443 participants (70.5%) tested, 11.6% were HIV positive. ART eligibility classification by the field and clinic checklists were concordant in 122 of 133 HIV-positive individuals. Compared with the clinic checklist, the field checklist had a sensitivity of 50% and a specificity of 96%. Including those already known to be on ART, staging by the field and clinic checklists estimated ART eligibility at 16.3 and 17.7% of HIV-positive individuals, respectively. Using CD4 cell count under 250 cells/mul or WHO stage III/IV, the Malawi national programme criteria, 38% of HIV-positive individuals were eligible for ART, compared with 31% based on the 2006 WHO criteria of CD4 cell count under 200 cells/mul or WHO stage IV or CD4 cell count of 200-350 cells/mul and WHO stage III. CONCLUSION: The field checklist was not a suitable tool for individual staging. Criteria for ART eligibility based on clinical staging alone missed two-thirds of those eligible by clinical staging and CD4 cell count
Population-level effect of HIV on adult mortality and early evidence of reversal after introduction of antiretroviral therapy in Malawi.
No full textBACKGROUND: Malawi, which has about 80,000 deaths from AIDS every year, made free antiretroviral therapy available to more than 80 000 patients between 2004 and 2006. We aimed to investigate mortality in a population before and after the introduction of free antiretroviral therapy, and therefore to assess the effects of such programmes on survival at the population level. METHODS: We used a demographic surveillance system to measure mortality in a population of 32,000 in northern Malawi, from August, 2002, when free antiretroviral therapy was not available in the study district, until February, 2006, 8 months after a clinic opened. Causes of death were established through verbal autopsies (retrospective interviews). Patients who registered for antiretroviral therapy at the clinic were identified and linked to the population under surveillance. Trends in mortality were analysed by age, sex, cause of death, and zone of residence. FINDINGS: Before antiretroviral therapy became available in June, 2005, mortality in adults (aged 15-59 years) was 9.8 deaths for 1000 person-years of observation (95% CI 8.9-10.9). The probability of dying between the ages of 15 and 60 years was 43% (39-49) for men and 43% (38-47) for women; 229 of 352 deaths (65.1%) were attributed to AIDS. 8 months after the clinic that provided antiretroviral therapy opened, 107 adults from the study population had accessed treatment, out of an estimated 334 in need of treatment. Overall mortality in adults had decreased by 10% from 10.2 to 8.7 deaths for 1000 person-years of observation (adjusted rate ratio 0.90, 95% CI 0.70-1.14). Mortality was reduced by 35% (adjusted rate ratio 0.65, 0.46-0.92) in adults near the main road, where mortality before antiretroviral therapy was highest (from 13.2 to 8.5 deaths per 1000 person-years of observation before and after antiretroviral therapy). Mortality in adults aged 60 years or older did not change. INTERPRETATION: Our findings of a reduction in mortality in adults aged between 15 and 59 years, with no change in those older than 60 years, suggests that deaths from AIDS were averted by the rapid scale-up of free antiretroviral therapy in rural Malawi, which led to a decline in adult mortality that was detectable at the population level
Competition between Jahn-Teller effect and spin-orbit coupling in T-d Au-20 (+/-gamma), gamma=1,2,3
No full textIn this work we explored the competition between spin-orbit and Jahn-Teller effects as decisive influences in the ground states of the T-d Au-20 (+/-gamma) (gamma=1,2,3). All our electronic calculations were based in the relativistic density functional theory in the zeroth-order regular approximation (ZORA) to the Dirac equation. Calculations were done in both versions of ZORA: scalar relativistic and full-relativistic including the spin-orbit interaction. We concluded that for the Au-20 (-3) ion is necessary to use a full-relativistic theory in order to predict a symmetry-lowering from tetrahedral. We predict a trigonal C-3v isomeric form for this trianion due to a Jahn-Teller distortion of its parent T-d. For the rest of ions we found a tendency to conserve their pristine tetrahedral configurations. In these cases we found one of both possibilities: a quenching of the vibronic interaction by spin-orbit coupling or simply a weak Jahn-Teller effect which is not enough to distort appreciably the cluster
CAS-SCF COMPUTATIONS ON JAHN-TELLER, RENNER-TELLER AND SECOND ORDER JAHN-TELLER SYSTEMS
No full textAuthor Institution: Department of Chemistry, King's College London, StrandThe information that can be obtained ab initio CAS-SCF computations on Jahn-Teller, Renner-Teller and second order Jahn-Teller systems will be presented in order to stimulate discussion of how this information can be used to rationalize experimental data. Several examples will be presented for each potential surface topology. The Jahn-Teller crossing and associated minima and saddle points were optimised for the cyclopentadienyl radical at the CASSCF/cc-p VDZ level of theory. The structures were characterised by computing analytic force constants. Zero point energies calculated for all and isomers of the minima suggest an alternative interpretation of the experimentally observed degeneracy resolution. For the benzene radical cation, the Jahn-Teller topology has also been mapped out. Finally, the use of symmetry in characterising the second order John-Teller effect will also be discussed for pentalene and cyclooctatetraene
Stabilization of A-type layered antiferromagnetic phase in LaMnO 3 by cooperative Jahn-Teller deformations
No full textPACS. 71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect - 75.30.Et Exchange and superexchange interactions,
Displacive Jahn--Teller transition in NaNiO
No full textBelow its Jahn--Teller transition temperature, , NaNiO has a monoclinic layered structure consisting of alternating layers of edge-sharing NaO and Jahn-Teller-distorted NiO octahedra. Above where NaNiO is rhombohedral, diffraction measurements show the absence of a cooperative Jahn-Teller distortion, accompanied by an increase in the unit cell volume. Using neutron total scattering, solid-state Nuclear Magnetic Resonance (NMR), and extended X-ray absorption fine structure (EXAFS) experiments as local probes of the structure we find direct evidence for a displacive, as opposed to order-disorder Jahn-Teller transition at . This is supported by \textit{ab initio} molecular dynamics (AIMD) simulations. To our knowledge this study is the first to show a displacive Jahn-Teller transition in any material using direct observations with local probe techniques.Under review. For SI, email the author
Noth-, Trost-und Hülfs-Büchlein gegen die Cholera morbus
No full textnach d. besten Quellen bearb. von J. R. M. Jahn [[vielm.] von Georg Wilhelm Jahn
Crucial role of Jahn-Teller distortions in LaMnO(3)
No full textThe crucial role of the cooperative Jahn-Teller deformations in determining the magnetic properties of stoechiometric LaMnO(3) is studied by means of exact diagonalization. The layered antiferromagnetic order mainly results from the strong cooperative Jahn-Teller deformations, stabilizing a certain type of orbital ordering. The main result is that antiferromagnetic (ferromagnetic) coupling along the c-direction (ab-planes) call be understood only if the Jahn-Teller energy is much larger than the superexchange couplings, which is consistent with experiments. The crucial role of the deformation anisotropy Q(2)/Q(3) is also emphasized: realistic values of Q(2)/Q(3) are needed to stabilize the layered order. The experimental values of the superxchange couplings can be recovered using reasonable sets of parameters. RI Grilli, Marco/C-6309-200
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