Interfacial surface roughness determination by coherence scanning interferometry using noise compensation.

The capability of coherence scanning interferometry has been extended recently to include the determination of the interfacial surface roughness between a thin film and a substrate when the surface perturbations are less than ∼10 nm in magnitude. The technique relies on introducing a first-order approximation to the helical complex field (HCF) function. This approximation of the HCF function enables a least-squares optimization to be carried out in every pixel of the scanned area to determine the heights of the substrate and/or the film layers in a multilayer stack. The method is fast but its implementation assumes that the noise variance in the frequency domain is statistically the same over the scanned area of the sample. This results in reconstructed surfaces that contain statistical fluctuations. In this paper we present an alternative least-squares optimization method, which takes into account the distribution of the noise variance-covariance in the frequency domain. The method is tested using results from a simulator and these show a significant improvement in the quality of the reconstructed surfaces.

Nonplanar Spray-Coated Perovskite Solar Cells.

Spray coating is an industrially mature technique used to deposit thin films that combines high throughput with the ability to coat nonplanar surfaces. Here, we explore the use of ultrasonic spray coating to fabricate perovskite solar cells (PSCs) over rigid, nonplanar surfaces without problems caused by solution dewetting and subsequent "run-off". Encouragingly, we find that PSCs can be spray-coated using our processes onto glass substrates held at angles of inclination up to 45° away from the horizontal, with such devices having comparable power conversion efficiencies (up to 18.3%) to those spray-cast onto horizontal substrates. Having established that our process can be used to create PSCs on surfaces that are not horizontal, we fabricate devices over a convex glass substrate, with devices having a maximum power conversion efficiency of 12.5%. To our best knowledge, this study represents the first demonstration of a rigid, curved perovskite solar cell. The integration of perovskite photovoltaics onto curved surfaces will likely find direct applications in the aerospace and automotive sectors.

Chlorine activated stacking fault removal mechanism in thin film CdTe solar cells: the missing piece.

The conversion efficiency of as-deposited, CdTe solar cells is poor and typically less than 5%. A CdCl2 activation treatment increases this to up to 22%. Studies have shown that stacking faults (SFs) are removed and the grain boundaries (GBs) are decorated with chlorine. Thus, SF removal and device efficiency are strongly correlated but whether this is direct or indirect has not been established. Here we explain the passivation responsible for the increase in efficiency but also crucially elucidate the associated SF removal mechanism. The effect of chlorine on a model system containing a SF and two GBs is investigated using density functional theory. The proposed SF removal mechanisms are feasible at the 400 ∘C treatment temperature. It is concluded that the efficiency increase is due to electronic effects in the GBs while SF removal is a by-product of the saturation of the GB with chlorine but is a key signal that sufficient chlorine is present for passivation to occur.

Understanding the Copassivation Effect of Cl and Se for CdTe Grain Boundaries.

Chlorine passivation treatment of cadmium telluride (CdTe) solar cells improves device performance by assisting electron-hole carrier separation at CdTe grain boundaries. Further improvement in device efficiency is observed after alloying the CdTe absorber layer with selenium. High-resolution secondary ion mass spectroscopy (NanoSIMS) imaging has been used to determine the distribution of selenium and chlorine at the CdTe grain boundaries in a selenium-graded CdTe device. Atomistic modeling based on density functional theory (DFT-1/2) further reveals that the presence of selenium and chlorine at an exemplar (110)/(100) CdTe grain boundary passivates critical acceptor defects and leads to n-type inversion at the grain boundary. The defect state analysis provides an explanation for the band-bending effects observed in the energy band alignment results, thereby elucidating mechanisms for high efficiencies observed in Se-alloyed and Cl-passivated CdTe solar cells.

Enhancement of photovoltaic efficiency in CdSe x Te1-x (where 0 ⩽ x ⩽ 1): insights from density functional theory.

Recent advancements in CdTe photovoltaic efficiency have come from selenium grading, which reduces the band gap and significantly improves carrier lifetimes. In this work, density functional theory calculations were performed to understand the structural and electronic effects of Se alloying. Special quasirandom structures were used to simulate a random distribution of Se anions. Lattice parameters decrease linearly as Se concentration increases in line with Vegard's Law. The simulated band gap bowing shows strong agreement with experimental values. Selenium, by itself, does not introduce any defect states in the band gap and no significant changes to band structure around the [Formula: see text] point are found. Band offset values suggest a reduction of recombination across the CdSeTe/MgZnO interface at [Formula: see text], which corresponds with the Se concentration used experimentally. Band structure analysis of two cases [Formula: see text] and x = 0.4375, shows a change from dominant Cd/Te contributions in the conduction band minimum to Cd/Se contributions as Se concentration is increased, hinting at a change in optical transition characteristics. Further calculations of optical absorption spectra suggest a reduced transition probability particularly at higher energies, which confirms experimental predictions that Se passivates the non-radiative recombination centres.

The EPSRC's Policy of Responsible Innovation from a Trading Zones Perspective.

Responsible innovation (RI) is gathering momentum as an academic and policy debate linking science and society. Advocates of RI in research policy argue that scientific research should be opened up at an early stage so that many actors and issues can steer innovation trajectories. If this is done, they suggest, new technologies will be more responsible in different ways, better aligned with what society wants, and mistakes of the past will be avoided. This paper analyses the dynamics of RI in policy and practice and makes recommendations for future development. More specifically, we draw on the theory of 'trading zones' developed by Peter Galison and use it to analyse two related processes: (i) the development and inclusion of RI in research policy at the UK's Engineering and Physical Sciences Research Council (EPSRC); (ii) the implementation of RI in relation to the Stratospheric Particle Injection for Climate Engineering (SPICE) project. Our analysis reveals an RI trading zone comprised of three quasi-autonomous traditions of the research domain - applied science, social science and research policy. It also shows how language and expertise are linking and coordinating these traditions in ways shaped by local conditions and the wider context of research. Building on such insights, we argue that a sensible goal for RI policy and practice at this stage is better local coordination of those involved and we suggest ways how this might be achieved.

Hydrazine-Free Solution-Deposited CuIn(S,Se)2 Solar Cells by Spray Deposition of Metal Chalcogenides.

Solution processing of semiconductors, such as CuInSe2 and its alloys (CIGS), can significantly reduce the manufacturing costs of thin film solar cells. Despite the recent success of solution deposition approaches for CIGS, toxic reagents such as hydrazine are usually involved, which introduce health and safety concerns. Here, we present a simple and safer methodology for the preparation of high-quality CuIn(S, Se)2 absorbers from metal sulfide solutions in a diamine/dithiol mixture. The solutions are sprayed in air, using a chromatography atomizer, followed by a postdeposition selenization step. Two different selenization methods are explored resulting in power conversion efficiencies of up to 8%.

Modelling the growth of ZnO thin films by PVD methods and the effects of post-annealing.

Results are presented for modelling of the evaporation and magnetron sputter deposition of Zn(x)O(y) onto an O-terminated ZnO (0001¯) wurtzite surface. Growth was simulated through a combination of molecular dynamics (MD) and an on-the-fly kinetic Monte Carlo (otf-KMC) method, which finds diffusion pathways and barriers without prior knowledge of transitions. We examine the effects of varying experimental parameters, such as substrate bias, distribution of the deposition species and annealing temperature. It was found when comparing evaporation and sputtering growth that the latter process results in a denser and more crystalline structure, due to the higher deposition energy of the arriving species. The evaporation growth also exhibits more stacking faults than the sputtered growth. Post-annealing at 770 K did not allow complete recrystallization, resulting in films which still had stacking faults where monolayers formed in the zinc blende phase, whereas annealing at 920 K enabled the complete recrystallization of some films to the wurtzite structure. At the latter temperature atoms could also sometimes be locked in the zinc blende phase after annealing. When full recrystallization did not take place, both wurtzite and zinc blende phases were seen in the same layer, resulting in a phase boundary. Investigation of the various distributions of deposition species showed that, during evaporation, the best quality film resulted from a stoichiometric distribution where only ZnO clusters were deposited. During sputtering, however, the best quality film resulted from a slightly O rich distribution. Two stoichiometric distributions, one involving mainly ZnO clusters and the other involving mainly single species, showed that the distribution of deposition species makes a huge impact on the grown film. The deposition of predominantly single species causes many more O atoms at the surface to be sputtered or reflected, resulting in an O deficiency of up to 18% in the deposited film and therefore resulting in more stacking faults and phase boundaries. The methods used allow analysis of key mechanisms that occur during the growth process and give hints as to the optimum conditions under which complete crystalline layers can form.

Risk, trust, and safety culture in U.K. train operating companies.

Organizational safety culture reflects the attitudes and behaviors that individuals share in considering and reacting to hazards and risks. We first argue that trust is an underdeveloped and important concept in relation to theories of safety culture and high-reliability organizations. The article then reports findings from a two-year qualitative study of train operating companies (TOCs) in the United Kingdom, which sought to explore in detail the linkages between safety culture and the postprivatized railway industry. In-depth interviews and focus groups were carried out with a sample of over 500 employees, from four organizations, and representing all key functional levels. Our analysis suggests that the 1993 privatization, and subsequent organizational restructuring of the U.K. railway industry, has had important repercussions for both safety culture and trust relationships. We explore our findings in relation to three key constructs within "safe organizations" theories (namely, flexibility, commitment, and learning), and discuss how the safe organization model might be usefully supplemented by a consideration of trust issues.

Using surveys in public participation processes for risk decision making: the case of the 2003 British GM Nation? Public debate.

This article takes as its case study the "GM Nation?" public debate, a major participation process on the commercialization of agricultural biotechnology, which occurred in Britain during the summer of 2003. We investigate possible self-selection biases in over 36,000 open questionnaire responses on the risks and benefits of genetically modified crops and food obtained during GM Nation? A comparison sample of equivalent responses from a statistically representative sample (n = 1,363) of the British general public obtained shortly after the conclusion of the debate is reported. This comparison shows that the GM Nation? open responses were indeed not fully representative of British "public opinion" regarding agricultural biotechnology. Rather, such opinion is not a unitary whole, but fragmented, with considerable ambivalence coexisting alongside outright opposition to GM agriculture. The methodological implications for multistage participation processes are discussed: in particular, the need to anticipate outcomes of complex design decisions, and to include representative public surveys as standard where measures of broader public attitudes to risk are an important objective.

Free amino acids mimic the anabolic but not the proliferative effect of albumin in OK proximal tubular cells.

When plasma proteins leak from circulation into the renal tubular lumen in the proteinuric renal diseases, nephrotoxicity of filtered albumin (and/or molecules bound to it) may be important in the subsequent development of tubulo-interstitial damage which contributes to the progression of the disease. When cultured opossum kidney (OK) proximal tubular cells were exposed to bovine serum albumin for 3 days in vitro, increased cell division ([3H]-thymidine incorporation) and cellular hypertrophy (increased protein/DNA ratio) were observed. Both effects were halved if defatted albumin was used. A trivial explanation for the growth responses is that free fatty acids carried on the albumin, and amino acids generated by intracellular degradation of the albumin, are exerting a non-specific growth effect as metabolic fuels which are oxidized to generate ATP. However, the water-soluble free fatty acid octanoate (1 mmol l(-1)) had no significant effect on protein/DNA ratio and a very variable stimulatory effect on [3H]-thymidine incorporation, whereas an essential amino acid mixture or 1 mmol/l(-1) l-Ala or l-Phe only increased the protein/DNA ratio. Furthermore no carnitine was added to the culture medium. This absence would have impaired mitochondrial transport (and hence oxidation) of long-chain free fatty acids derived from the albumin. l-Phe is also a poor substrate for mitochondrial oxidation in kidney. It is therefore concluded that the growth effects of albumin in OK proximal tubular cells are specific effects of the albumin protein and of the free fatty acids and amino acids derived from it, and not a non-specific effect on metabolic fuel supply.

Acidosis downregulates leptin production from cultured adipocytes through a glucose transport-dependent post-transcriptional mechanism.

Metabolic acidosis, a common feature of uremia, has a well documented wasting effect on skeletal muscle. In contrast, the effect of metabolic acidosis on adipose tissue is unknown. Serum levels of the adipocyte hormone leptin have been shown to be lower in acidotic uremic rats when compared with uremic controls. This study investigated the effect of acidosis on leptin protein secretion and leptin gene expression. This was studied in vitro by means of 3T3-L1 cultured adipocytes. Leptin secretion was decreased at an acid pH of 7.1 compared with a control pH of 7.5 (1277 versus 1950 pg/well/48 h, P < 0.05). In contrast, acidosis did not affect leptin mRNA content. Glucose transport was reduced by 39% at pH 7.1 at 24 h, which was comparable in magnitude with the inhibition of leptin secretion at the same pH. The glucose transport inhibitors cytochalasin B (0.5 to 50 micro M) and phloretin (0.05 to 0.25 mM) mimicked the effect of acidosis and reduced leptin secretion in a dose-dependent fashion (P < 0.02). Dose-response curves for the inhibition of glucose uptake showed that decreasing glucose transport to the same extent as with acid was sufficient to drive down leptin secretion, independently of changes of leptin mRNA. Acid decreases leptin secretion from 3T3-L1 adipocytes through a post-transcriptional mechanism via changes in glucose transport. This starvation-like response may be physiologically important in conditions such as uremia to prevent excessive energy expenditure.

Stimulation of protein degradation by low pH in L6G8C5 skeletal muscle cells is independent of apoptosis but dependent on differentiation state.

BACKGROUND: In chronic renal failure, metabolic acidosis increases protein degradation (PD) in skeletal muscle, an effect which in vivo requires glucocorticoid (GC). This disorder is poorly understood, but can be studied in vitro using L6G8C5 rat skeletal muscle cells. Two potential confounding factors in studies of PD in culture are apoptosis and dedifferentiation, both of which resemble catabolic states. The aim of this study was to determine the extent to which these factors contribute to the observed effects of acid and GC on PD. METHODS: PD was measured in intact cells by pre-labelling cell protein with [(14)C]phenylalanine. Apoptosis was assessed morphologically by staining DNA with Hoechst 33342, by terminal deoxynucleotide transferase-mediated nick-end labelling and by cell-surface binding of Annexin V. Differentiation was assessed morphologically from myotube fusion and from activity of the marker enzyme creatine phosphokinase (CPK). RESULTS: In undifferentiated myoblasts, pH had no detectable effect on apoptosis provided that serum was present and GC (dexamethasone; 5 nmol/l) decreased apoptosis. In spontaneously fused cultures in 2% serum, inhibition of apoptosis with caspase-3 inhibitor (C3I; Ac-Asp-Met-Gln-Asp-CHO; 50 micro mol/l) only decreased PD by 9% at pH 7.4. In contrast, the proteasome inhibitor MG132 decreased PD by 79%. Acid (pH 7.1) increased PD, with no requirement for GC, and this effect was blocked by MG132, but not by C3I. Differentiation was unaffected by 1-4 days of exposure to acid or GC. However, differentiation to myotubes led to decreased sensitivity of PD to acid. This effect of acid was lost completely in highly fused myotubes, but was partly restored by 500 nmol/l dexamethasone. CONCLUSIONS: Stimulation of PD in these cells by acid and GC is not an artefact of apoptosis or dedifferentiation, but differentiation state does determine whether PD responds spontaneously to acid or (as in vivo) only does so in the presence of GC.

Nutrition in CAPD: serum bicarbonate and the ubiquitin-proteasome system in muscle.

BACKGROUND: Metabolic acidosis in chronic renal failure (CRF) induces loss of lean body mass while elimination of acidosis during a one year trial improved anthropometric indices in continuous ambulatory peritoneal dialysis (CAPD) patients. In rats with CRF, the mechanisms causing loss of lean body mass have been linked to acidosis-induced destruction of the essential, branched-chain amino acids (BCAA) and activation of the ubiquitin-proteasome system that degrades muscle protein; the latter response includes increased transcription of the ubiquitin gene. METHOD: Our aim was to determine if increasing the serum bicarbonate (HCO3) concentration of CAPD patients would improve their nutritional status, increase plasma BCAA levels, and reduce ubiquitin mRNA in their muscle as an index of suppressed activity of the ubiquitin-proteasome system. Eight, stable, long-term CAPD patients underwent vastus lateralis muscle biopsy before being randomized to continue 35 mmol/L lactate dialysate or convert to a 40 mmol/L lactate dialysate. After four weeks, measurements were repeated. RESULTS: Serum HCO3 increased in all patients and final values did not differ statistically between the two groups so results for all patients were combined. Weight and body mass index increased significantly as did plasma BCAA. Muscle levels of ubiquitin mRNA decreased significantly; serum tumor necrosis factor-alpha (TNF-alpha) also decreased. CONCLUSION: Our results indicate that even a small correction of serum HCO3 improves nutritional status, and provide evidence for down-regulation of BCAA degradation and muscle proteolysis via the ubiquitin-proteasome system. Whether acidosis and inflammatory cytokines (such as, TNF-alpha) interact to impair nutrition is unknown.

Fatty acids carried on albumin modulate proximal tubular cell fibronectin production: a role for protein kinase C.

BACKGROUND: Proteinuric renal disease is associated with accumulation of tubulointerstitial matrix proteins. Human proximal tubular cells (PTCs) produce fibronectin in response to serum proteins but not albumin alone. It has been suggested that renal toxicity of filtered albumin depends on its lipid moiety. We therefore investigated the functional consequences of different fatty acids (FAs) carried on human albumin after exposure to human PTCs in culture. METHODS: Confluent human PTCs were exposed to recombinant human serum albumin (rHSA) or palmitate (P)-, stearate (S)-, oleate (O)-, and linoleate (L)-complexed rHSA. In all experimental conditions, test media contained 1 mg/ml rHSA alone or carrying 100 mmol FAs. Mitogenic response was assessed by [(3)H]thymidine incorporation. Cell culture supernatants were assayed for fibronectin. Protein kinase C (PKC) activity was assessed in cell lysates. RESULTS: Apical exposure to rHSA alone or the O-rHSA complex stimulated a significant increase in [(3)H]thymidine incorporation, whereas the L-rHSA complex was markedly inhibitory to human PTC growth. The L-rHSA complex was associated with severe cytotoxicity as assessed by lactate dehydrogenase release. Among all conditions, O-rHSA was the only test media that significantly increased fibronectin levels over control conditions (150.1+/-10.6% over control, P<0.05, n=3). Pre-treatment of PTCs with PKC inhibitors before O-rHSA exposure resulted in a dose-dependent decrease in fibronectin secretion. O-rHSA activated PKC significantly compared with controls. CONCLUSIONS: We conclude that rHSA has a mitogenic effect on human PTCs, but fibronectin secretion was only induced by O-complexed rHSA and the O-rHSA effect was mediated via PKC activation. Involvement of PKC signal transduction pathway may be a novel therapeutic target for ameliorating proteinuria-induced tubular injury.

Fatty acids exacerbate tubulointerstitial injury in protein-overload proteinuria.

The role of the albumin-carried fatty acids in the induction of tubulointerstitial injury was studied in protein-overload proteinuria. Rats were injected with fatty acid-carrying BSA [FA(+)BSA], fatty acid-depleted BSA [FA(-)BSA], or saline. Macrophage infiltration was measured by immunohistochemical staining, apoptotic cells were detected by in situ end labeling, and proliferating cells were identified by in situ hybridization for histone mRNA. Macrophage infiltration was significantly greater in the FA(+)BSA group than in the FA(-)BSA and saline groups. The infiltrate was largely restricted to the outer cortex. Apoptosis was greater in the FA(+)BSA group than in the FA(-)BSA and saline groups. Compared with the saline group, apoptosis was significantly increased in the FA(+)BSA group but not in the FA(-)BSA group. Cortical cells proliferated significantly more in the FA(+)BSA and FA(-)BSA groups than in the saline group. FA(+)BSA is therefore a more potent inducer of macrophage infiltration and cell death than FA(-)BSA. The fatty acids carried on albumin may be the chief instigators of tubulointerstitial injury in protein-overload proteinuria.

Glucocorticoid antagonist RU38486 fails to block acid-induced muscle wasting in vivo or in vitro.

BACKGROUND: Increased protein degradation during metabolic acidosis contributes to muscle wasting in uraemia. Adrenalectomy experiments in severely acidotic rats (arterial pH approximately 7.15) have shown that this is prevented in the absence of glucocorticoid. It should therefore be possible to block such muscle wasting with glucocorticoid receptor antagonist 11beta-(4-dimethylaminophenyl)-17beta-hydroxy,-17a-(prop-1-ynyl)-estra-4,9-dien-3-one (RU38486). METHODS: The effect of oral RU38486 (50 mg/kg body weight/day) was studied in vivo by administration to rats receiving dietary HCl supplements which yielded moderate acidosis (plasma HCO(3)(-) 19.7 +/- 1.2 mmol/l), comparable with that observed in uraemia. The effect of the glucocorticoid dexamethasone (DEX) (up to 500 nmol/l) and RU38486 (up to 5 micro mol/l) was also studied in vitro in acidified cultures of L6-G8C5 rat skeletal muscle cells. RESULTS: In vivo 15 days of moderate acidosis slowed weight gain and induced muscle wasting (6% weight loss in gastrocnemius with a commensurate decline in muscle protein) but, at this level of acidosis, muscle protein degradation showed no detectable increase. Wasting was not inhibited by RU38486 in spite of blockade of 80% of the glucocorticoid receptors in gastrocnemius. Unexpectedly, weight gain was significantly slower in acidotic rats receiving RU38486 than in acidotic rats receiving vehicle. In vitro acid spontaneously stimulated protein degradation, but even under strongly acidic conditions (pH 7.1) this was only weakly and transiently stimulated by 5 nmol/l DEX and transiently blunted by 5 micro mol/l RU38486. In contrast, as little as 1 nmol/l insulin-like growth factor I (IGF-I) almost abolished the effect of acid and this was partly restored by 5 nmol/l DEX. CONCLUSIONS: IGF-I is a potent determinant of acid-induced protein degradation in vitro and is antagonized by glucocorticoid. If glucocorticoid acts in this indirect way in vivo this may explain why, in moderate metabolic acidosis with intact adrenal glands, the action of RU38486 via glucocorticoid is too weak to be of therapeutic value.

Specific, sensitive, and quantitative enzyme-linked immunosorbent assay for human immunoglobulin G antibodies to anthrax toxin protective antigen.

The bioterrorism-associated human anthrax epidemic in the fall of 2001 highlighted the need for a sensitive, reproducible, and specific laboratory test for the confirmatory diagnosis of human anthrax. The Centers for Disease Control and Prevention developed, optimized, and rapidly qualified an enzyme-linked immunosorbent assay (ELISA) for immunoglobulin G (IgG) antibodies to Bacillus anthracis protective antigen (PA) in human serum. The qualified ELISA had a minimum detection limit of 0.06 micro g/mL, a reliable lower limit of detection of 0.09 micro g/mL, and a lower limit of quantification in undiluted serum specimens of 3.0 micro g/mL anti-PA IgG. The diagnostic sensitivity of the assay was 97.8%, and the diagnostic specificity was 97.6%. A competitive inhibition anti-PA IgG ELISA was also developed to enhance diagnostic specificity to 100%. The anti-PA ELISAs proved valuable for the confirmation of cases of cutaneous and inhalational anthrax and evaluation of patients in whom the diagnosis of anthrax was being considered.