High sensitivity of 17O NMR to p-d hybridization in transition metal perovskites: first principles calculations of large anisotropic chemical shielding

A first principles embedded cluster approach is used to calculate O chemical shielding tensors, sigma, in prototypical transition metal oxide ABO_3 perovskite crystals. Our principal findings are 1) a large anisotropy of sigma between deshielded sigma_x ~ sigma_y and shielded sigma_z components (z along the Ti-O bond); 2) a nearly linear variation, across all the systems studied, of the isotropic sigma_iso and uniaxial sigma_ax components, as a function of the B-O-B bond asymmetry. We show that the anisotropy and linear variation arise from large paramagnetic contributions to sigma_x and sigma_y due to virtual transitions between O(2p) and unoccupied B(nd) states. The calculated isotropic delta_iso and uniaxial delta_ax chemical shifts are in good agreement with recent BaTiO_3 and SrTiO_3 single crystal 17O NMR measurements. In PbTiO_3 and PbZrO_3, calculated delta_iso are also in good agreement with NMR powder spectrum measurements. In PbZrO_3, delta_iso calculations of the five chemically distinct sites indicate a correction of the experimental assignments. The strong dependence of sigma on covalent O(2p)-B(nd) interactions seen in our calculations indicates that 17O NMR spectroscopy, coupled with first principles calculations, can be an especially useful tool to study the local structure in complex perovskite alloys.Comment: 12 pages, 3 figures, and 3 Table

Prevalence and correlates of prehypertension and hypertension among adults in Delta State, Nigeria: a cross-sectional community-based study

Background: There are indications that prehypertension precedes hypertension. Like hypertension, it is associated with increased cardiovascular risk. Objective: To determine the prevalence, awareness and correlates of prehypertension and hypertension among adults in Delta State, Nigeria. Methods: This was a cross-sectional study. We recruited adults aged ≥18 years from two communities in Delta State, Nigeria, using the multi-stage sampling technique. The study instrument was a modified WHO-STEPS questionnaire.Prehypertension and hypertension were defined using the JNC-7 criteria. Ethical approval was obtained before the recruitment of participants. Results: Of the 852 adults studied, the mean (±SD) age was 42.64 (±16.07) years, females (55.9%) and urban dwellers (55.8%). The prevalence of prehypertension and hypertension were 42.5% and 29.3%, respectively; both were higheramong urban dwellers. The peak age-group for prehypertension and hypertension were 25-34 and 35-44 years, respectively.Awareness of hypertension was low; 12.0% (102/852). Blood pressure category significantly correlated with age, body mass index, place of residence, level of education, employment status and fruit intake. Conclusion: The prevalence of prehypertension and hypertension in this study were high. Based on the premise that prehypertension is a precursor of hypertension and occurred more among youths, the higher prevalence of prehypertensiongives an inkling to rising prevalence of hypertension. Keywords: Prehypertension, hypertension, adults, Nigeria, WHO STEPS Funding: Ni

Prevalence and correlates of prehypertension and hypertension among adults in Delta State, Nigeria: a cross-sectional community-based study

Background: There are indications that prehypertension precedes hypertension. Like hypertension, it is associated with increased cardiovascular risk.Objective: To determine the prevalence, awareness and correlates of prehypertension and hypertension among adults in Delta State, Nigeria. Methods: This was a cross-sectional study. We recruited adults aged ≥18 years from two communities in Delta State, Nigeria, using the multi-stage sampling technique. The study instrument was a modified WHO-STEPS questionnaire.Prehypertension and hypertension were defined using the JNC-7 criteria. Ethical approval was obtained before the recruitment of participants. Results: Of the 852 adults studied, the mean (±SD) age was 42.64 (±16.07) years, females (55.9%) and urban dwellers (55.8%). The prevalence of prehypertension and hypertension were 42.5% and 29.3%, respectively; both were higheramong urban dwellers. The peak age-group for prehypertension and hypertension were 25-34 and 35-44 years, respectively. Awareness of hypertension was low; 12.0% (102/852). Blood pressure category significantly correlatedwith age, body mass index, place of residence, level of education, employment status and fruit intake. Conclusion: The prevalence of prehypertension and hypertension in this study were high. Based on the premise that prehypertension is a precursor of hypertension and occurred more among youths, the higher prevalence of prehypertensiongives an inkling to rising prevalence of hypertension. Keywords: Prehypertension, hypertension, adults, Nigeria, WHO STEPS Funding: Ni

Neural synchronization is strongest to the spectral flux of slow music and depends on familiarity and beat salience

Neural activity in the auditory system synchronizes to sound rhythms, and brain–environment synchronization is thought to be fundamental to successful auditory perception. Sound rhythms are often operationalized in terms of the sound’s amplitude envelope. We hypothesized that – especially for music – the envelope might not best capture the complex spectro-temporal fluctuations that give rise to beat perception and synchronized neural activity. This study investigated (1) neural synchronization to different musical features, (2) tempo-dependence of neural synchronization, and (3) dependence of synchronization on familiarity, enjoyment, and ease of beat perception. In this electroencephalography study, 37 human participants listened to tempo-modulated music (1–4 Hz). Independent of whether the analysis approach was based on temporal response functions (TRFs) or reliable components analysis (RCA), the spectral flux of music – as opposed to the amplitude envelope – evoked strongest neural synchronization. Moreover, music with slower beat rates, high familiarity, and easy-to-perceive beats elicited the strongest neural response. Our results demonstrate the importance of spectro-temporal fluctuations in music for driving neural synchronization, and highlight its sensitivity to musical tempo, familiarity, and beat salience

XMM-Newton observations of HD189733 during planetary transits

We report on two XMM-Newton observations of the planetary host star HD189733. The system has a close in planet and it can potentially affect the coronal structure via interactions with the magnetosphere. We have obtained X-ray spectra and light curves from EPIC and RGS on board XMM-Newton which we have analyzed and interpreted. We reduced X-ray data from primary transit and secondary eclipse occurred in April 17th 2007 and May 18th 2009, respectively. In the April 2007 observation only variability due to weak flares is recognized. In 2009 HD189733 exhibited a X-ray flux always larger than in the 2007 observation. The average flux in 2009 was higher than in 2007 observation by a factor of 45%. During the 2009 secondary eclipse we observed a softening of the X-ray spectrum significant at level of ~3 sigma. Further, we observed the most intense flare recorded at either epochs. This flare occurred 3 ks after the end of the eclipse.The flare decay shows several minor ignitions perhaps linked to the main event and hinting for secondary loops that emit triggered by the main loop. Magneto-Hydro-Dynamical (MHD) simulations show that the magnetic interaction between planet and star enhances the density and the magnetic field in a region comprised between the planet and the star because of their relative orbital/rotation motion. X-ray observations and model predictions are globally found in agreement, despite the quite simple MHD model and the lack of precise estimate of parameters including the alignment and the intensity of stellar and planetary magnetic fields. Future observations should confirm or disprove this hypothesis, by determining whether flares are systematically recurring in the light curve at the same planetary phase.Comment: Accepted for publication on The Astrophysical Journa

Surface excitonic emission and quenching effects in ZnO nanowire/nanowall systems: limiting effects on device potential.

We report ZnO nanowire/nanowall growth using a two-step vapour phase transport method on a-plane sapphire. X-ray diffraction and scanning electron microscopy data establish that the nanostructures are vertically well-aligned with c-axis normal to the substrate, and have a very low rocking curve width. Photoluminescence data at low temperatures demonstrate the exceptionally high optical quality of these structures, with intense emission and narrow bound exciton linewidths. We observe a high energy excitonic emission at low temperatures close to the band-edge which we assign to the surface exciton in ZnO at ~ 3.366 eV, the first time this feature has been reported in ZnO nanorod systems. This assignment is consistent with the large surface to volume ratio of the nanowire systems and indicates that this large ratio has a significant effect on the luminescence even at low temperatures. The band-edge intensity decays rapidly with increasing temperature compared to bulk single crystal material, indicating a strong temperature-activated non-radiative mechanism peculiar to the nanostructures. No evidence is seen of the free exciton emission due to exciton delocalisation in the nanostructures with increased temperature, unlike the behaviour in bulk material. The use of such nanostructures in room temperature optoelectronic devices appears to be dependent on the control or elimination of such surface effects