Kinetics and Mechanisms of Photoelectrochemical Reactions at Semiconductor Electrodes

Some kinetic aspects of the photocurrent response of semiconductor electrodes are considered. Particular attention is given to surface recombination, which reduces the photocurrent conversion efficiency, and to photocurrent multiplication, which leads to quantum efficiencies greater than unity. The advantages of non steady-state photocurrent measurements are considered, and it is shown that the coupling of electron and hole fluxes via the surface leads to a characteristic time or frequency dependence of the photocurrent conversion efficiency. The principle of intensity modulated photocurrent spectroscopy (IMPS) is described, and its application is illustrated with several examples, including the reduction of oxygen at p-GaAs and the photooxidation of Si in NH4F. It is shown that frequency response analysis offers unique insights into complex photoelectrode processes of this kind

Genome-wide patterns of carbon and nitrogen regulation of gene expression validate the combined carbon and nitrogen (CN)-signaling hypothesis in plants

BACKGROUND: Carbon and nitrogen are two signals that influence plant growth and development. It is known that carbon- and nitrogen-signaling pathways influence one another to affect gene expression, but little is known about which genes are regulated by interactions between carbon and nitrogen signaling or the mechanisms by which the different pathways interact. RESULTS: Microarray analysis was used to study global changes in mRNA levels due to carbon and nitrogen in Arabidopsis thaliana. An informatic analysis using InterAct Class enabled us to classify genes on the basis of their responses to carbon or nitrogen treatments. This analysis provides in vivo evidence supporting the hypothesis that plants have a carbon/nitrogen (CN)-sensing/regulatory mechanism, as we have identified over 300 genes whose response to combined CN treatment is different from that expected from expression values due to carbon and nitrogen treatments separately. Metabolism, energy and protein synthesis were found to be significantly affected by interactions between carbon and nitrogen signaling. Identified putative cis-acting regulatory elements involved in mediating CN-responsive gene expression suggest multiple mechanisms for CN responsiveness. One mechanism invokes the existence of a single CN-responsive cis element, while another invokes the existence of cis elements that promote nitrogen-responsive gene expression only when present in combination with a carbon-responsive cis element. CONCLUSION: This study has allowed us to identify genes and processes regulated by interactions between carbon and nitrogen signaling and take a first step in uncovering how carbon- and nitrogen-signaling pathways interact to regulate transcription

A benchmarking study of two trauma centres highlighting limitations when standardising mortality for comorbidity

<p>Abstract</p> <p>Introduction</p> <p>A continuous process of trauma centre evaluation is essential to ensure the development and progression of trauma care at regional, national and international levels. Evaluation may be by comparison between pooled datasets or by direct benchmarking between centres. This study attempts to benchmark mortality at two trauma centres standardising this for multiple case-mix factors, which includes the prevalence of individual background pre-existing diseases within the study population.</p> <p>Methods</p> <p>Trauma patients with an Injury Severity Score (ISS) >15 admitted to the two centres in 2001 and 2002 were included in the study with the exception of those who died in the emergency department. Patient characteristics were analysed in terms of 18 case-mix factors including Glasgow Coma Scale on arrival, Injury Severity Score and the presence or absence of 9 co-morbidity types, and patient outcome was compared based on in-hospital mortality before and after standardisation.</p> <p>Results</p> <p>Crude mortality was greater at UHNS (18.2 vs 14.5%) with a non-significant odds ratio of 1.31 prior to adjusting for case-mix (P = 0.171). Adjustment for case mix using logistic regression analysis altered the odds ratio to 1.64, which was not significant (P = 0.069).</p> <p>Discussion</p> <p>This study did not demonstrate any significant difference in the outcome of patients treated at either hospital during the study period. More importantly it has raised several important methodological issues pertinent to researchers undertaking registry based benchmarking studies. Data at the two registries was collected by personnel with differing backgrounds, in formats that were not completely compatible and was collected for patients that met different admissions criteria. The inclusion of a meaningful analysis of pre-existing disease was limited by the availability of robust data and sample size. We suggest greater communication between trauma research coordinators to ensure equivalent data collection and facilitate future benchmarking studies.</p

Expressed in the yeast Saccharomyces cerevisiae, human ERK5 is a client of the Hsp90 chaperone that complements loss of the Slt2p (Mpk1p) cell integrity stress-activated protein kinase

ERK5 is a mitogen-activated protein (MAP) kinase regulated in human cells by diverse mitogens and stresses but also suspected of mediating the effects of a number of oncogenes. Its expression in the slt2Delta Saccharomyces cerevisiae mutant rescued several of the phenotypes caused by the lack of Slt2p (Mpk1p) cell integrity MAP kinase. ERK5 is able to provide this cell integrity MAP kinase function in yeast, as it is activated by the cell integrity signaling cascade that normally activates Slt2p and, in its active form, able to stimulate at least one key Slt2p target (Rlm1p, the major transcriptional regulator of cell wall genes). In vitro ERK5 kinase activity was abolished by Hsp90 inhibition. ERK5 activity in vivo was also lost in a strain that expresses a mutant Hsp90 chaperone. Therefore, human ERK5 expressed in yeast is an Hsp90 client, despite the widely held belief that the protein kinases of the MAP kinase class are non-Hsp90-dependent activities. Two-hybrid and protein binding studies revealed that strong association of Hsp90 with ERK5 requires the dual phosphorylation of the TEY motif in the MAP kinase activation loop. These phosphorylations, at positions adjacent to the Hsp90-binding surface recently identified for a number of protein kinases, may cause a localized rearrangement of this MAP kinase region that leads to creation of the Hsp90-binding surface. Complementation of the slt2Delta yeast defect by ERK5 expression establishes a new tool with which to screen for novel agonists and antagonists of ERK5 signaling as well as for isolating mutant forms of ERK5

Exploratory studies to inform full-scale evaluations of complex public health interventions: the need for guidance

No abstract available

X-ray Diffraction Analysis of Stratum Corneum Membrane Couplets

X-ray diffraction analysis was done on the membrane couplets isolated from newborn mouse stratum corneum. The same lipid reflections were observed for whole stratum corneum and couplets, adding further support to the thesis that stratum corneum lipid is intercellular in location rather than associated with the intracellular filamentous protein

Characterization of cadmium sulfide buffer layers using electrolyte contacts

© 2018 Elsevier B.V. Electrolyte contacts were used to characterize cadmium sulfide (CdS) films grown by chemical bath deposition on fluorine-doped tin oxide glass (FTO). Capacitance measurements were made in a buffered electrolyte free of redox species, and cyclic sweep voltammetry was carried out using an electrolyte containing Fe(CN)64− ions. A theoretical model was developed to describe the influence of pinholes on Mott Schottky plots of CdS-coated FTO. The model allows estimation of the pinhole coverage by fitting the Mott Schottky plot over an extended voltage range. Cyclic voltammetry in a hexacyanoferrate(II) electrolyte also allows detection of pinholes, but quantitative estimation of pinhole coverage is complicated by the fact that diffusion of Fe(CN)64− to pinholes occurs by hemispherical diffusion, which can substantially enhance the current response. Comparison of the results of capacitance and voltammetry measurements provides insights into average pore size and number density. Results presented for CdS films grown using two different chemical bath compositions reveal substantial differences in pinhole numbers and doping density

Interpretation of photocurrent transients at semiconductor electrodes:Effects of band-edge unpinning

The transient photocurrent response of semiconductor electrodes to chopped illumination often shows spikes and overshoots that are usually interpreted as evidence that surface recombination is occurring. In the case of the high intensities used for light-driven water splitting, the interpretation is less straightforward since the electron transfer reactions are so slow that the minority carrier concentration at or near the surface increases to high values that modify the potential drop across the Helmholtz layer in the electrolyte, leading to ‘band edge unpinning’. In addition, changes in chemical composition of the surface or local changes in pH may also alter the potential distribution across the semiconductor/electrolyte junction. A quantitative theory of band edge unpinning due to minority carrier build up is presented, and numerical calculations of transient photocurrent responses are compared with experimental examples for n-type Fe2O3 and p-type lithium-doped CuO electrodes. It is shown that the apparently high reaction orders (up to third order) with respect to hole concentration reported for hematite photoanodes can be explained as arising from an acceleration of hole transfer by the increased voltage drop across the Helmholtz layer associated with band edge unpinning. The limitations of the band edge unpinning model are discussed considering additional effects associated with modification of the potential distribution brought about by light-induced changes in surface composition, surface dipoles and surface ionic charge.</p