79 research outputs found
Superconductivity at 5 K in potassium doped phenanthrene
Organic materials are believed to be potential superconductor with high
transition temperature (TC). Organic superconductors mainly have two families:
the quasi-one dimensional (TMTSF)2X and two dimensional (BEDT-TTF)2X (Ref. 1
and 2), in which TMTSF is tetramethyltetraselenafulvalene (C10H12Se4) and
BEDT-TTF or "ET" is bis(ethylenedithio)tetrathiafulvalene (C10H8S8). One key
feature of the organic superconductors is that they have {\pi}-molecular
orbitals, and the {\pi}-electron can delocalize throughout the crystal giving
rise to metallic conductivity due to a {\pi}-orbital overlap between adjacent
molecules. The introduction of charge into C60 solids and graphites with
{\pi}-electron networks by doping to realize superconductivity has been
extensively reported3,4. Very recently, superconductivity in alkali-metal doped
picene with {\pi}-electron networks was reported5. Here we report the discovery
of superconductivity in potassium doped Phenanthrene with TC~5 K. TC increases
with increasing pressure, and the pressure of 1 GPa leads to an increase of 20%
in TC, suggesting that the potassium doped phenanthrene shows unconventional
superconductivity. Both phenanthrene and picene are polycyclic aromatic
hydrocarbons, and contain three and five fused benzene rings, respectively. The
ribbon of fused benzene rings is part of graphene. Therefore, the discovery of
superconductivity in K3Phenanthrene produces a novel broad class of
superconductors consisting of fused hydrocarbon benzene rings with
{\pi}-electron networks. The fact that TC increases from 5 K for KxPhenanthrene
with three benzene rings to 18 K for Kxpicene with five benzene rings suggests
that such organic hydrocarbons with long benzene rings is potential
superconductor with high TC.Comment: 20 pages, 3 figures, one supplementary information. submitted to
Nature Communication
Random-phase approximation and its applications in computational chemistry and materials science
The random-phase approximation (RPA) as an approach for computing the
electronic correlation energy is reviewed. After a brief account of its basic
concept and historical development, the paper is devoted to the theoretical
formulations of RPA, and its applications to realistic systems. With several
illustrating applications, we discuss the implications of RPA for computational
chemistry and materials science. The computational cost of RPA is also
addressed which is critical for its widespread use in future applications. In
addition, current correction schemes going beyond RPA and directions of further
development will be discussed.Comment: 25 pages, 11 figures, published online in J. Mater. Sci. (2012
Low-energy unphysical saddle in polynomial molecular potentials
Vibrational spectra of polyatomic molecules are often obtained from a
polynomial expansion of the adiabatic potential around a minimum. For several
molecules, we show that such an approximation displays an unphysical saddle
point of comparatively small energy, leading to a region where the potential is
negative and unbounded. This poses an upper limit for a reliable evaluation of
vibrational levels. We argue that the presence of such saddle points is
general.Comment: The preprint version of the published Mol. Phys. paper, 19 pages, 3
figure
Cross-Location Analysis of the Impact of Household Socioeconomic Status on Participation in Urban and Peri-Urban Agriculture in West Africa
This study explores the relation between household socioeconomic status (SES) and participation in urban and periurban agriculture (UPA) in three West African cities. We used a structured questionnaire to survey 700 randomly selected households: 250 in Kano, Nigeria, 250 in Bobo Dioulasso, Burkina Faso, and 200 in Sikasso, Mali. Multiple correspondence analysis was applied on household asset variables to create an index of assets which was used as a proxy for household SES. The results showed no significant differences in households’ rate of participation in UPA across socioeconomic groups. Participation in UPA was rather significantly (P < 0.001) and positively related to household size. Interestingly, the analysis revealed that field crop cultivation and gardening were more common among households in the low and medium SES groups while those in the high SES group were more likely to keep livestock
Where should patients with or at risk of delirium be treated in an acute care system? Comparing the rates of delirium in patients receiving usual care versus alternative care : a systematic review and meta‐analysis
Background:
Delirium is an acute condition that occurs in hospitalised patients and leads to poor patient outcomes that can last long term. Therefore, the importance of prevention is undeniable and adopting new models of care for at risk patients should be prioritised.
Objectives:
This systematic review and meta‐analysis will assess the effectiveness of different interventions designed to prevent or manage delirium in acutely unwell hospitalised patients.
Methods:
MEDLINE, EMBASE, PsychINFO, OpenGrey, Web of Science and reference lists of journals were searched. Eligible studies reported on incidence or duration of delirium, used a validated delirium diagnostic tool, and compared an intervention to either a control or another intervention group. Meta‐analyses were conducted, and GRADE pro software was used to assess the certainty of evidence. This review is registered on PROSPERO.
Results:
A total of 59 studies were included and 33 were eligible for meta‐analysis. Delirium incidence was most significantly reduced by non‐pharmacological multicomponent interventions compared to usual care, with pooled risk ratios of 0.57 (95% CI: 0.44 to 0.73, ten randomised controlled trials) and 0.47 (95% CI: 0.35 to 0.64, six observational studies). Single component interventions did not significantly reduce delirium incidence compared to usual care in seven randomised trials (risk ratio= 0.92, 95% CI: 0.81 to 1.04). The most effective single component intervention in reducing delirium incidence, was a hospital‐at‐home intervention (risk ratio = 0.29, 95% CI: 0.09 to 0.87).
Conclusions:
Non‐pharmacological multicomponent interventions are effective in preventing delirium, however the same cannot be said for other interventions due to uncertain results. There is some evidence that providing multicomponent interventions in patients’ homes is more effective than a hospital setting. Therefore, researching the benefits of hospital‐at‐home interventions in delirium prevention is recommended
Link between microbial composition and carbon substrate-uptake preferences in a PHA-storing community
The microbial community of a fermented molasses-fed sequencing batch reactor (SBR) operated under feast and famine conditions for production of polyhydroxyalkanoates (PHAs) was identified and quantified through a 16 S rRNA gene clone library and fluorescence in situ hybridization (FISH). The microbial enrichment was found to be composed of PHA-storing populations (84% of the microbial community), comprising members of the genera Azoarcus, Thauera and Paracoccus. The dominant PHA-storing populations ensured the high functional stability of the system (characterized by high PHA-storage efficiency, up to 60% PHA content). The fermented molasses contained primarily acetate, propionate, butyrate and valerate. The substrate preferences were determined by microautoradiography-FISH and differences in the substrate-uptake capabilities for the various probe-defined populations were found. The results showed that in the presence of multiple substrates, microbial populations specialized in different substrates were selected, thereby co-existing in the SBR by adapting to different niches. Azoarcus and Thauera, primarily consumed acetate and butyrate, respectively. Paracoccus consumed a broader range of substrates and had a higher cell-specific substrate uptake. The relative species composition and their substrate specialization were reflected in the substrate removal rates of different volatile fatty acids in the SBR reactor
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