Electron affinities of the first- and second- row atoms: benchmark ab initio and density functional calculations

A benchmark ab initio and density functional (DFT) study has been carried out on the electron affinities of the first- and second-row atoms. The ab initio study involves basis sets of $spdfgh$ and $spdfghi$ quality, extrapolations to the 1-particle basis set limit, and a combination of the CCSD(T), CCSDT, and full CI electron correlation methods. Scalar relativistic and spin-orbit coupling effects were taken into account. On average, the best ab initio results agree to better than 0.001 eV with the most recent experimental results. Correcting for imperfections in the CCSD(T) method improves the mean absolute error by an order of magnitude, while for accurate results on the second-row atoms inclusion of relativistic corrections is essential. The latter are significantly overestimated at the SCF level; for accurate spin-orbit splitting constants of second-row atoms inclusion of (2s,2p) correlation is essential. In the DFT calculations it is found that results for the 1st-row atoms are very sensitive to the exchange functional, while those for second-row atoms are rather more sensitive to the correlation functional. While the LYP correlation functional works best for first-row atoms, its PW91 counterpart appears to be preferable for second-row atoms. Among ``pure DFT'' (nonhybrid) functionals, G96PW91 (Gill 1996 exchange combined with Perdew-Wang 1991 correlation) puts in the best overall performance. The best results overall are obtained with the 1-parameter hybrid modified Perdew-Wang (mPW1) exchange functionals of Adamo and Barone [J. Chem. Phys. {\bf 108}, 664 (1998)], with mPW1LYP yielding the best results for first-row, and mPW1PW91 for second-row atoms. Indications exist that a hybrid of the type $a$ mPW1LYP + $(1-a)$ mPW1PW91 yields better results than either of the constituent functionals.Comment: Phys. Rev. A, in press (revised version, review of issues concerning DFT and electron affinities added

An exactly solvable model of a superconducting to rotational phase transition

We consider a many-fermion model which exhibits a transition from a superconducting to a rotational phase with variation of a parameter in its Hamiltonian. The model has analytical solutions in its two limits due to the presence of dynamical symmetries. However, the symmetries are basically incompatible with one another; no simple solution exists in intermediate situations. Exact (numerical) solutions are possible and enable one to study the behavior of competing but incompatible symmetries and the phase transitions that result in a semirealistic situation. The results are remarkably simple and shed light on the nature of phase transitions.Comment: 11 pages including 1 figur

Temporal correlation between malaria and rainfall in Sri Lanka

<p>Abstract</p> <p>Background</p> <p>Rainfall data have potential use for malaria prediction. However, the relationship between rainfall and the number of malaria cases is indirect and complex.</p> <p>Methods</p> <p>The statistical relationships between monthly malaria case count data series and monthly mean rainfall series (extracted from interpolated station data) over the period 1972 – 2005 in districts in Sri Lanka was explored in four analyses: cross-correlation; cross-correlation with pre-whitening; inter-annual; and seasonal inter-annual regression.</p> <p>Results</p> <p>For most districts, strong positive correlations were found for malaria time series lagging zero to three months behind rainfall, and negative correlations were found for malaria time series lagging four to nine months behind rainfall. However, analysis with pre-whitening showed that most of these correlations were spurious. Only for a few districts, weak positive (at lags zero and one) or weak negative (at lags two to six) correlations were found in pre-whitened series. Inter-annual analysis showed strong negative correlations between malaria and rainfall for a group of districts in the centre-west of the country. Seasonal inter-annual analysis showed that the effect of rainfall on malaria varied according to the season and geography.</p> <p>Conclusion</p> <p>Seasonally varying effects of rainfall on malaria case counts may explain weak overall cross-correlations found in pre-whitened series, and should be taken into account in malaria predictive models making use of rainfall as a covariate.</p

Evaluation of appendicitis risk prediction models in adults with suspected appendicitis

Background Appendicitis is the most common general surgical emergency worldwide, but its diagnosis remains challenging. The aim of this study was to determine whether existing risk prediction models can reliably identify patients presenting to hospital in the UK with acute right iliac fossa (RIF) pain who are at low risk of appendicitis. Methods A systematic search was completed to identify all existing appendicitis risk prediction models. Models were validated using UK data from an international prospective cohort study that captured consecutive patients aged 16–45 years presenting to hospital with acute RIF in March to June 2017. The main outcome was best achievable model specificity (proportion of patients who did not have appendicitis correctly classified as low risk) whilst maintaining a failure rate below 5 per cent (proportion of patients identified as low risk who actually had appendicitis). Results Some 5345 patients across 154 UK hospitals were identified, of which two‐thirds (3613 of 5345, 67·6 per cent) were women. Women were more than twice as likely to undergo surgery with removal of a histologically normal appendix (272 of 964, 28·2 per cent) than men (120 of 993, 12·1 per cent) (relative risk 2·33, 95 per cent c.i. 1·92 to 2·84; P < 0·001). Of 15 validated risk prediction models, the Adult Appendicitis Score performed best (cut‐off score 8 or less, specificity 63·1 per cent, failure rate 3·7 per cent). The Appendicitis Inflammatory Response Score performed best for men (cut‐off score 2 or less, specificity 24·7 per cent, failure rate 2·4 per cent). Conclusion Women in the UK had a disproportionate risk of admission without surgical intervention and had high rates of normal appendicectomy. Risk prediction models to support shared decision‐making by identifying adults in the UK at low risk of appendicitis were identified

A study on CdCl2 activation of CBD-CdS films

Cadmium sulfide (CdS) thin films were deposited using chemical bath deposition (CBD) technique on fluorine-doped tin oxide glass substrates. Cadmium sulfate, thiourea, and ammonium hydroxide were used as Cd source, S source, and the complexing agent, respectively in the reaction bath. The post-deposition CdCl2 activation of chemical bath deposited CdS (CBD-CdS) thin films was done by dip coating in a saturated CdCl2 bath. X-ray diffractograms show the growth of large CdS grains with better crystalline quality over the recrystallization process due to CdCl2 treatment. The development of large clusters was determined to be due to coalescence of smaller clusters. The photoelectrochemical (PEC) cell (CdS/Na2S2O3/Pt) parameters, such as VOC and ISC for CdCl2 activated CBD-CdS thin films were found to be higher compared to untreated CBD-CdS thin films. The improved effective surface area of the film and higher carrier concentration due to grain boundary passivation could be the reason for higher VOC and ISC values found in CdCl2-treated CdS films. Additionally, all the CdCl2-treated CdS films showed an increase in the optical transmittance spectra and bandgap compared to untreated CdS films. Relative energy band edge position of the grown CdS films was found to be adjustable with the CdCl2 treatment time. The best photoactivity was found for the CdS films which were dip-coated for 10 min in CdCl2 solution

Growth and Characterization of Seed-Assisted, EDTA-Treated, Chemical Bath-Deposited CdS

Abstract: A simple low-cost method to enhance the electrical properties including open-circuit voltage (VOC), flat-band potential (Vfb) and short-circuit current (ISC) in the photoelectrochemical (PEC) cell of cadmium sulfide (CdS) thin films is presented. The PEC cell properties were determined using the configuration Pt/0.1 M Na2S2O3/CdS. Three different sets of CdS thin films were grown: (a) chemical bath-deposited CdS (CBD-CdS), (b) electrodeposited seed-assisted CBD-CdS (ED/CBD-CdS) and (c) ED/CBD-CdS deposited under the presence of ethylenediaminetetraacetic acid (EDTA) in a reaction solution of CBD (ED/(CBD+EDTA)-CdS). The FE-SEM images suggested the formation of clusters with spherical shape in the presence of a seed layer. All the samples grown with seed layers demonstrated improved ISC and VOC values in the PEC cell compared to the CBD-CdS films due to better contact between the substrate and CBD-CdS. Furthermore, the carrier concentration (ND) and Vfb were also found to improve due to the introduction of the seed layer. In the case of ED/(CBD+EDTA)-CdS, the cluster size was found to be smaller, giving rise to a larger effective surface area. The improved effective surface area, interparticle connections and adhesion of CdS to the FTO substrate resulted in superior electrical properties of ED/(CBD+EDTA)-CdS compared to ED/CBD-CdS and CBD-CdS films. Graphical Abstract: [Figure not available: see fulltext.

Evolution of nanoripples on silicon by gas cluster-ion irradiation

Si wafers of (100), (110) and (111) orientations were bombarded by gas cluster ion beam (GCIB) of 3000 Ar-atoms/cluster on average at a series of angles. Similar surface morphology ripples developed in different nanoscales. A simple scaling functional satisfactorily describe the roughness and wavelength of the ripple patterns as a function of dosage and angle of incidence. The ripples are formed orthogonal to the incident cluster-ions at large off-normal angles. An ellipsoidal pattern was created by two consecutive irradiations incident in mutually orthogonal directions with unequal exposure times between each irradiation, from 7:1 to 10:1, beyond which the original ripple imprints would be over-written. This work was inspired by use of the ripples to seed growth of controlled nanostructures without patterning by lithography or predeposition of catalysts