Efficient solar cells are more stable: The impact of polymer molecular weight on performance of organic photovoltaics

The principle remaining challenge in the research area of organic photovoltaic (OPV) materials is to develop solar cells that combine high efficiency, stability and reproducibility. Here, we demonstrate an experimental strategy which has successfully addressed this challenge. We produced a number of samples of the highly efficient PTB7 polymer with various molecular weights (Mn 40–220k). OPV cells fabricated with this polymer demonstrated significant improvement of the cell efficiency (by 90% relative) and lifetime (by 300% relative) with the Mn increase. We attribute these effects to the lower density of recombination centers (persistent radical defects revealed by EPR spectroscopy) and better photoactive layer morphology in the samples with higher Mn. Relevance of the observed correlation between the OPV efficiency and stability is discussed

QUantitative Imaging of eXtraction of oxygen and TIssue consumption (QUIXOTIC) using venular-targeted velocity-selective spin labeling

available in PMC 2012 December 1While oxygen extraction fraction (OEF) and cerebral metabolic rate of oxygen (CMRO2) are fundamental parameters of brain health and function, a robust MRI-based mapping of OEF and CMRO2 amenable to functional MRI (fMRI) has not been established. To address this issue, a novel method called QUantitative Imaging of eXtraction of Oxygen and TIssue Consumption, or QUIXOTIC, is introduced. The key innovation in QUIXOTIC is the use of velocity-selective spin labeling to isolate MR signal exclusively from postcapillary venular blood on a voxel-by-voxel basis. Measuring the T2 of this venular-targeted blood allows calibration to venular oxygen saturation (Yv) via theoretical and experimental T2 versus blood oxygen saturation relationships. Yv is converted to OEF, and baseline CMRO2 is subsequently estimated from OEF and additional cerebral blood flow and hematocrit measurements. Theory behind the QUIXOTIC technique is presented, and implications of cutoff velocity (VCUTOFF) and outflow time parameters are discussed. Cortical gray matter values obtained with QUIXOTIC in 10 healthy volunteers are Yv = 0.73 ± 0.02, OEF = 0.26 ± 0.02, and CMRO2 = 125 ± 15 μmol/100 g min. Results are compared to global measures obtained with the T2 relaxation under spin tagging (TRUST) technique. The preliminary data presented suggest that QUIXOTIC will be useful for mapping Yv, OEF, and CMRO2, in both clinical and functional MRI settings.National Institutes of Health (U.S.) (NIH Neuroimaging Training Program Grant, 5-T32-EB001680)National Institutes of Health (U.S.) (NIH Neuroimaging Training Program Grant, 5-R01-EB002066-20)National Institutes of Health (U.S.) (Center for Functional Neuroimaging Technologies; Grant number: P41RR14075S10RR023401)Siemens Aktiengesellschaft (Siemens Medical Solutions)Harvard University--MIT Division of Health Sciences and Technology (Martinos Catalyst Fund)National Cancer Institute (U.S.) (NIH Grant number RO1 EB007942)National Institutes of Health (U.S.) (NIH Medical Scientist Training Program Fellowship, grant no. T32-GM07753

Infections with Avian Pathogenic and Fecal Escherichia coli Strains Display Similar Lung Histopathology and Macrophage Apoptosis

The purpose of this study was to compare histopathological changes in the lungs of chickens infected with avian pathogenic (APEC) and avian fecal (Afecal) Escherichia coli strains, and to analyze how the interaction of the bacteria with avian macrophages relates to the outcome of the infection. Chickens were infected intratracheally with three APEC strains, MT78, IMT5155, and UEL17, and one non-pathogenic Afecal strain, IMT5104. The pathogenicity of the strains was assessed by isolating bacteria from lungs, kidneys, and spleens at 24 h post-infection (p.i.). Lungs were examined for histopathological changes at 12, 18, and 24 h p.i. Serial lung sections were stained with hematoxylin and eosin (HE), terminal deoxynucleotidyl dUTP nick end labeling (TUNEL) for detection of apoptotic cells, and an anti-O2 antibody for detection of MT78 and IMT5155. UEL17 and IMT5104 did not cause systemic infections and the extents of lung colonization were two orders of magnitude lower than for the septicemic strains MT78 and IMT5155, yet all four strains caused the same extent of inflammation in the lungs. The inflammation was localized; there were some congested areas next to unaffected areas. Only the inflamed regions became labeled with anti-O2 antibody. TUNEL labeling revealed the presence of apoptotic cells at 12 h p.i in the inflamed regions only, and before any necrotic foci could be seen. The TUNEL-positive cells were very likely dying heterophils, as evidenced by the purulent inflammation. Some of the dying cells observed in avian lungs in situ may also be macrophages, since all four avian E. coli induced caspase 3/7 activation in monolayers of HD11 avian macrophages. In summary, both pathogenic and non-pathogenic fecal strains of avian E. coli produce focal infections in the avian lung, and these are accompanied by inflammation and cell death in the infected areas

Air Exposure Induced Recombination in PTB7:PC₇₁BM Solar Cells

SAJT acknowledges studentship funding from EPSRC under grant number EP/G03673X/1. I. D. W. S. acknowledges support EPSRC (EP/L012294/1) and a Royal Society Wolfson Research Merit Award. S. C. H. acknowledges funding from EPSRC under grant number EP/J500045/1. We also acknowledge support from the Wellcome Trust (099149) and from EPSRC (EP/F039034/1)Understanding degradation pathways in organic photovoltaic cells (OPV) is essential to achieve long term device stability and allow commercialisation. Upon exposure to an ambient atmosphere the power conversion efficiency (PCE) of PTB7:PC71BM solar cells, cast using the solvent additive DIO, is markedly reduced. Using electrically detected magnetic resonance (EDMR) spectroscopy, trap sites, which are formed when the blend is exposed to air and DIO, are identified. Spin-Rabi oscillations reveal that the resonance arises from a weakly coupled pair of spin 1/2 species, while selective injection of charge carriers into the cell demonstrates that the spin-pair corresponds to recombination of electrons and holes. The recombination is assigned to holes on the PTB7 recombining with electrons localised to oxygen induced PC71BM trap sites.Publisher PDFPeer reviewe

Comparative indoor and outdoor stability measurements of polymer based solar cells

We report comparative indoor and outdoor stability testing of organic solar cells based on a blend between a donor-acceptor polyfluorene copolymer and a fullerene derivative. The outdoor testing was conducted for a period over 12,000 hours in Sheffield, England, with a Ts80 lifetime determined in excess of 10,000 hours (420 days). Indoor lifetime testing was performed on solar cells using a solar simulator under a constant irradiance of 1000 W/m(2) for more than 650 hours. We show that under the conditions explored here, device degradation under the two sets of conditions is approximately dependent on the absorbed optical energy dose

Cosmological neutrinos

The current status of neutrino cosmology is reviewed, from the question of neutrino decoupling and the presence of sterile neutrinos to the effects of neutrinos on the cosmic microwave background and large scale structure. Particular emphasis is put on cosmological neutrino mass measurements.Comment: 21 pages, 4 figures, review for NJP focus issue on neutrino

Balancing repair and tolerance of DNA damage caused by alkylating agents

Alkylating agents constitute a major class of frontline chemotherapeutic drugs that inflict cytotoxic DNA damage as their main mode of action, in addition to collateral mutagenic damage. Numerous cellular pathways, including direct DNA damage reversal, base excision repair (BER) and mismatch repair (MMR), respond to alkylation damage to defend against alkylation-induced cell death or mutation. However, maintaining a proper balance of activity both within and between these pathways is crucial for a favourable response of an organism to alkylating agents. Furthermore, the response of an individual to alkylating agents can vary considerably from tissue to tissue and from person to person, pointing to genetic and epigenetic mechanisms that modulate alkylating agent toxicity

The diversity of myeloid immune cells shaping wound repair and fibrosis in the lung

In healthy circumstances the immune system coordinates tissue repair responses in a tight balance that entails efficient inflammation for removal of potential threats, proper wound closure, and regeneration to regain tissue function. Pathological conditions, continuous exposure to noxious agents, and even ageing can dysregulate immune responses after injury. This dysregulation can lead to a chronic repair mechanism known as fibrosis. Alterations in wound healing can occur in many organs, but our focus lies with the lung as it requires highly regulated immune and repair responses with its continuous exposure to airborne threats. Dysregulated repair responses can lead to pulmonary fibrosis but the exact reason for its development is often not known. Here, we review the diversity of innate immune cells of myeloid origin that are involved in tissue repair and we illustrate how these cell types can contribute to the development of pulmonary fibrosis. Moreover, we briefly discuss the effect of age on innate immune responses and therefore on wound healing and we conclude with the implications of current knowledge on the avenues for future research

Pectinmethylesterase from the rice weevil, Sitophilus oryzae: cDNA isolation and sequencing, genetic origin, and expression of the recombinant enzyme

A cDNA clone encoding pectinmethylesterase of the rice weevil, Sitophilus oryzae (L.) has been isolated and sequenced. The cDNA clone was expressed in cultured insect cells and active pectinmethylesterase was purified from the culture medium, thus confirming that the cDNA encodes pectinmethylesterase. In situ hybridization indicated that the enzyme's transcript was present in the midgut. Weevils treated with tetracycline so that they lack genes of known symbiotic organisms still contained the pectinmethylesterase gene, indicating that the gene is encoded by the rice weevil genome. The rice weevil enzyme is most similar in sequence to bacterial pectinmethylesterases. Given this and the enzyme's apparently rather general absence from animal species, we suggest the possibility that this gene was transferred horizontally to an ancient weevil, possibly from a bacterial symbiont, and exists in Sitophilus species now as a result of that ancestral horizontal transfer

Genome-wide analysis identifies 12 loci influencing human reproductive behavior.

The genetic architecture of human reproductive behavior-age at first birth (AFB) and number of children ever born (NEB)-has a strong relationship with fitness, human development, infertility and risk of neuropsychiatric disorders. However, very few genetic loci have been identified, and the underlying mechanisms of AFB and NEB are poorly understood. We report a large genome-wide association study of both sexes including 251,151 individuals for AFB and 343,072 individuals for NEB. We identified 12 independent loci that are significantly associated with AFB and/or NEB in a SNP-based genome-wide association study and 4 additional loci associated in a gene-based effort. These loci harbor genes that are likely to have a role, either directly or by affecting non-local gene expression, in human reproduction and infertility, thereby increasing understanding of these complex traits