N-Aryl stilbazolium dyes as sensitizers for solar cells

Eight new N-arylstilbazolium chromophores with electron donating -NR₂ (R = Me or Ph) substituents have been synthesized via Knoevenagel condensations and isolated as their PF₆⁻ salts. These compounds have been characterized by using various techniques including ¹H NMR and IR spectroscopies and electrospray mass spectrometry. UV-vis absorption spectra recorded in acetonitrile are dominated by intense, low energy π → π* intramolecular charge-transfer (ICT) bands, and replacing Me with Ph increases the ICT energies. Cyclic voltammetric studies show irreversible reduction processes, together with oxidation waves that are irreversible for R = Me, but reversible for R = Ph. Single crystal X-ray structures have been determined for three of the methyl ester-substituted stilbazolium salts and for the Cl⁻ salts of their picolinium precursors. Time-dependent density functional theory calculations afford reasonable predictions of ICT energies, but greater rigour is necessary for -NPh₂ derivatives. The four new acid-functionalized dyes give moderate sensitization efficiencies (ca. 0.2%) when using TiO₂-based photoanodes, with relatively higher values for R = Ph vs Me, while larger efficiencies (up to 0.8%) are achieved with ZnO substrates.     

The creation and evaluation of a model predicting the probability of conception in seasonal-calving,pasture-based dairy cows

Reproductive performance in pasture-based production systems has a fundamentally important effect on economic efficiency. The individual factors affecting the probability of submission and conception are multifaceted and have been extensively researched. The present study analyzed some of these factors in relation to service-level probability of conception in seasonal-calving pasture-based dairy cows to develop a predictive model of conception. Data relating to 2,966 services from 737 cows on 2 research farms were used for model development and data from 9 commercial dairy farms were used for model testing, comprising 4,212 services from 1,471 cows. The data spanned a 15-yr period and originated from seasonal-calving pasture-based dairy herds in Ireland. The calving season for the study herds extended from January to June, with peak calving in February and March. A base mixed-effects logistic regression model was created using a stepwise model-building strategy and incorporated parity, days in milk, interservice interval, calving difficulty, and predicted transmitting abilities for calving interval and milk production traits. To attempt to further improve the predictive capability of the model, the addition of effects that were not statistically significant was considered, resulting in a final model composed of the base model with the inclusion of BCS at service. The models' predictions were evaluated using discrimination to measure their ability to correctly classify positive and negative cases. Precision, recall, F-score, and area under the receiver operating characteristic curve (AUC) were calculated. Calibration tests measured the accuracy of the predicted probabilities. These included tests of overall goodness-of-fit, bias, and calibration error. Both models performed better than using the population average probability of conception. Neither of the models showed high levels of discrimination (base model AUC 0.61, final model AUC 0.62), possibly because of the narrow central range of conception rates in the study herds. The final model was found to reliably predict the probability of conception without bias when evaluated against the full external data set, with a mean absolute calibration error of 2.4%. The chosen model could be used to support a farmer's decision-making and in stochastic simulation of fertility in seasonal-calving pasture-based dairy cows.     

Alfred Swaine Taylor (1801–80)

Abstract

After a period in decline the Portobello Road market in London has enjoyed a revival in the past two or three years. There are at least three dealers in historic photographs within fifty yards of an East Anglian couple who regularly bring good quality decorative antiques and other curios to sell on Saturday mornings. I stopped at their showcase, looked in, walked on, and then returned to take a second look at a scrapbook, so often a source of good printed ephemera. It was open at a page showing a comic drawing of a wagon done up as an itinerant photographer's studio. I was told how much the scrapbook was and spent the next ten minutes looking through it. I decided on balance that I could ‘just about see the price in it’ ignoring the four photographs, which I believed must be of little or no value. On reaching my car I had another look through the album. A negative image of a leaf (figure 1) looked interesting, for a few months earlier I had been to Lacock and now remembered Talbot's photogenic drawings. Examination of the engravings and lithographs showed that they started in the 1820s and ended in 1853. This was undoubtedly a girl's scrapbook begun when she was quite small and probably continued until her early teens when the enthusiasm for pasting was bound to wane. I settled on a probable year of birth of 1840 for the girl but most careful combing discovered no name or initials in the book. There were, however, some postcards celebrating a pageant in 1907 at Bury St Edmunds, Suffolk, and one had been posted to a Mrs F. Methold at an address in Bury, but how she was connected with the book remained to be disovered. I looked once more through the printed ephemera and spotted that two cards with heavily embossed borders had small hand-coloured lithographs pasted on to them. My suspicion that these were early Victorian invitations proved to be correct. Removing the little pictures revealed that they were invitations from the Pharmaceutical Society to Alfred S. Taylor, FRS, to attend two dinners dated May 1848 and July 1849. I did not think that it was straining common sense to conclude that father had given his daughter these old invitations for her scrapbook.     

Diamagnetic levitation enhances growth of liquid bacterial cultures by increasing oxygen availability

Diamagnetic levitation is a technique that uses a strong, spatially varying magnetic field to reproduce aspects of weightlessness, on the Earth. We used a superconducting magnet to levitate growing bacterial cultures for up to 18 h, to determine the effect of diamagnetic levitation on all phases of the bacterial growth cycle. We find that diamagnetic levitation increases the rate of population growth in a liquid culture and reduces the sedimentation rate of the cells. Further experiments and microarray gene analysis show that the increase in growth rate is owing to enhanced oxygen availability. We also demonstrate that the magnetic field that levitates the cells also induces convective stirring in the liquid. We present a simple theoretical model, showing how the paramagnetic force on dissolved oxygen can cause convection during the aerobic phases of bacterial growth. We propose that this convection enhances oxygen availability by transporting oxygen around the liquid culture. Since this process results from the strong magnetic field, it is not present in other weightless environments, e.g. in Earth orbit. Hence, these results are of significance and timely to researchers considering the use of diamagnetic levitation to explore effects of weightlessness on living organisms and on physical phenomena.