Exciton Regeneration at Polymeric Semiconductor Heterojunctions

Control of the band-edge offsets at heterojunctions between organic semiconductors allows efficient operation of either photovoltaic or light-emitting diodes. We investigate systems where the exciton is marginally stable against charge separation, and show via E-field-dependent time-resolved photoluminescence spectroscopy that excitons that have undergone charge separation at a heterojunction can be efficiently regenerated. This is because the charge transfer produces a geminate electron-hole pair (separation 2.2-3.1nm) which may collapse into an exciplex and then endothermically (E=100-200meV) back-transfer towards the exciton.Comment: 10 pages, 4 figures. Manuscript in press in Phys. Rev. Let

Preliminary genetic evidence of two different populations of Opisthorchis viverrini in Lao PDR

Opisthorchis viverrini is a major public health concern in Southeast Asia. Various reports have suggested that this parasite may represent a species complex, with genetic structure in the region perhaps being dictated by geographical factors and different species of intermediate hosts. We used four microsatellite loci to analyze O. viverrini adult worms originating from six species of cyprinid fish in Thailand and Lao PDR. Two distinct O. viverrini populations were observed. In Ban Phai, Thailand, only one subgroup occurred, hosted by two different fish species. Both subgroups occurred in fish from That Luang, Lao PDR, but were represented to very different degrees among the fish hosts there. Our data suggest that, although geographical separation is more important than fish host specificity in influencing genetic structure, it is possible that two species of Opisthorchis, with little interbreeding, are present near Vientiane in Lao PDR

Time to Switch to Second-line Antiretroviral Therapy in Children With Human Immunodeficiency Virus in Europe and Thailand.

Background: Data on durability of first-line antiretroviral therapy (ART) in children with human immunodeficiency virus (HIV) are limited. We assessed time to switch to second-line therapy in 16 European countries and Thailand. Methods: Children aged <18 years initiating combination ART (≥2 nucleoside reverse transcriptase inhibitors [NRTIs] plus nonnucleoside reverse transcriptase inhibitor [NNRTI] or boosted protease inhibitor [PI]) were included. Switch to second-line was defined as (i) change across drug class (PI to NNRTI or vice versa) or within PI class plus change of ≥1 NRTI; (ii) change from single to dual PI; or (iii) addition of a new drug class. Cumulative incidence of switch was calculated with death and loss to follow-up as competing risks. Results: Of 3668 children included, median age at ART initiation was 6.1 (interquartile range (IQR), 1.7-10.5) years. Initial regimens were 32% PI based, 34% nevirapine (NVP) based, and 33% efavirenz based. Median duration of follow-up was 5.4 (IQR, 2.9-8.3) years. Cumulative incidence of switch at 5 years was 21% (95% confidence interval, 20%-23%), with significant regional variations. Median time to switch was 30 (IQR, 16-58) months; two-thirds of switches were related to treatment failure. In multivariable analysis, older age, severe immunosuppression and higher viral load (VL) at ART start, and NVP-based initial regimens were associated with increased risk of switch. Conclusions: One in 5 children switched to a second-line regimen by 5 years of ART, with two-thirds failure related. Advanced HIV, older age, and NVP-based regimens were associated with increased risk of switch

Culture of fecal indicator bacteria from snail intestinal tubes as a tool for assessing the risk of Opisthorchis viverrini infection in Bithynia snail habitat

Abstract Background Like many trematodes of human health significance, the carcinogenic liver fluke, Opisthorchis viverrini, is spread via fecal contamination of snail habitat. Methods for assessing snail exposure to fecal waste can improve our ability to identify snail infection hotspots and potential sources of snail infections. We evaluated the feasibility of culturing fecal indicator bacteria from Bithynia snail intestinal tubes as a method for assessing snail exposure to fecal waste. Snails and water samples were collected from a site with a historically high prevalence of O. viverrini infected snails (“hotspot” site) and a site with historically no infected snails (“non-hotspot” site) on two sampling days. Snails were tested for O. viverrini and a stratified random sample of snails from each site was selected for intestinal tube removal and culture of gut contents for the fecal indicator bacteria, Escherichia coli. Water samples were tested for E. coli and nearby households were surveyed to assess sources of fecal contamination. Results At the hotspot site, 26 of 2833 Bithynia siamensis goniomphalos snails were infected with O. viverrini compared to 0 of 1421 snails at the non-hotspot site. A total of 186 snails were dissected and cultured. Escherichia coli were detected in the guts of 20% of uninfected snails, 4% of O. viverrini-positive snails and 8% of snails not examined for cercarial infection at the hotspot site. Only one of 75 snails from the non-hotspot site was positive for E. coli. Accounting for sampling weights, snails at the hotspot site were more likely to have gut E. coli than snails from the non-hotspot site. The concentration of fecal indicator bacteria in surface water was higher at the hotspot vs non-hotspot site on only the first sampling day. Conclusions Fecal indicator bacteria can be detected in the intestinal tubes of Bithynia snails. The presence of fecal indicator bacteria in Bithynia snail guts may indicate risk of O. viverrini infection in snail populations. This method has the potential to aid in identifying locations and time windows of peak snail infection risk and may be applicable to other trematodes of human-health significance

Reliability analysis of beams on random elastic foundations

The classical problem of a beam on an elastic foundation has long been of practical interest to geotechnical engineers, because it provides a framework for computing deflections not only of foundations, but also of vertically oriented laterally loaded piles. The supporting soil can be modelled as an elastic medium, which can be calibrated to represent the stiffness of the soils adjacent to the beam (or pile). The objective of this paper is to study the influence of spatially random soil stiffness on deformations of transversely loaded homogeneous piles and beams, using a combination of finiteelement analysis, random field theory and Monte Carlo simulations. Following code validation against alternative solutions, the method investigates how the statistically defined soil stiffness (mean, standard deviation and spatial correlation length) influences the mean and standard deviation of pile or beam deflection. The goal of such an approach is to estimate the probability of deflections exceeding some design threshold.Geoscience & EngineeringCivil Engineering and Geoscience

Toward Designed Singlet Fission: Electronic States and Photophysics of 1,3-Diphenylisobenzofuran

Single crystal molecular structure and solution photophysical properties are reported for 1,3-diphenylisobenzofuran (1), of interest its a model compound in studies of singlet fission. For the ground state of I and of its radical cation (1(+center dot)) and anion (1(-center dot)), we report the UV-visible absorption spectra, and for neutral 1, also the magnetic circular dichroism (MCD) and the decomposition of the absorption spectrum into purely polarized components, deduced from fluorescence polarization. These results were used to identify a series of singlet excited states. For the first excited singlet and triplet states of 1, the transient visible absorption spectra, S-1 -> S-x and sensitized T-1 -> T-x and single exponential lifetimes, tau(F) = similar to 5.3 ns and tau(T) = similar to 200 mu s, are reported. The spectra and lifetimes of S-1 -> S-0 fluorescence and sensitized T-1 -> T-x absorption of I were obtained in a series of solvents, as was the fluorescence quantum yield, Phi(F) = 0.95-0.99, No phosphorescence has been detected. The first triplet excitation energy of solid I (11 400 cm(-1)) was obtained by electron energy loss spectroscopy, in agreement with previously reported solution values. The fluorescence excitation spectrum suggests all onset of a nonradiative channel at similar to 37 000 cm(-1). Excitation energies and relative transition intensities are in agreement with those of ab initio (CC2) calculations after all empirical 3000 cm(-1) adjustment of the initial state energy to Correct differentially for a better quality description of the initial relative to the terminal suite of in absorption transition. The interpretation of the MCD spectrum used the semiempirical PPP method, whose results for the S-1 -> S-x spectrum require no empirical adjustment and are otherwise nearly identical with the CC2 results in all respects including the detailed nature of the electronic excitation. The ground state geometry of I Was also Calculated by the MP2, B3LYP, and CAS methods. The calculations provided a prediction of changes of molecular geometry upon excitation or ionization and permitted all interpretation of the spectra in tern-is of molecular orbitals involved. Computations suggest that 1 call exist as two nearly isoenergetic conformers of C-2 or C-x symmetry. Linear dichroism measurements in stretched polyethylene provide evidence for their existence and show that they orient to different degrees, permitting a separation of their spectra in the region Of the purely polarized first absorption band. Their excitation energies are nearly identical, but the Franck-Condon envelopes of their first transition differ to a surprising degree