Improving solar cell performance through surface modification of silicon

This project sets out to improve the efficiency of thin crystalline silicon solar cells by enhancing the photoexcitation through light harvesting, and by developing a novel surface passivation technique via the covalent attachment of organic molecules to the surface. To aid the characterisation of these novel structures, we have developed a new measurement technique for surface recombination using the Kelvin prove.A passivation method through the attachment of alkyl monolayers to the silicon surface has been developed. These layers were shown to have good passivation properties whilst retaining excellent resilience to oxidation. The passivation effect was determined to be caused by the generation of surface charge, as measured by the Kelvin probe. Further functionalisation of the organic monolayers was undertaken to attach fluorescent chromophores. A novel method for measurement of the surface recombination velocity was developed utilising the Kelvin probe. Changing the incident photon flux, and thus the photogenerated current, allows measurement of the surface recombination current through the change in surface photovoltage. This dependence can then be used to extract the value of the surface recombination velocity. Furthermore, we have shown that this method can be developed further into a mapping technique for surface recombination lifetime, of potentially significant industrial interest.The effect of the silicon surface charge on the passivation observed has been investigated through the attachment of charged monolayers. It was found that through the attachment of a positive charge, the observed recombination lifetime in n-type silicon decreased whilst a negative charge (through the attachment of carboxylic acid groups to the surface) was found to improve the surface passivation. The carboxylic acid functional groups were charged through immersion in triethylamine (base) and returned to the neutral, starting state through immersion in acetic acid. We have found that the recombination lifetime decreases linearly with decreasing charge-surface distance. This technique allows an in-depth study of surface passivation to be carried out by separating the two principal causes for passivation – the removal of surface states and charge attachment to the surface.Fluorescent chromophores were attached to the silicon surface by two different techniques – through the reaction of an alcohol-terminated monolayer with an acyl chloride porphyrin and by palladium-catalysed cross-coupling of an allyl-terminated surface with a cyanine dye. The fluorescence quenching was investigated at various chromophore-silicon distances by varying the length of the alkyl chain spacer. We find that the fluorescence lifetime decreases with decreasing chromophore-silicon distance, and follows a logarithmic trend. Further work is required, however, to combine sensitisation with surface passivation as incorporation of a sensitisation layer by the palladium cross coupling of an allyl-terminated surface results in metal contamination to the surface, reducing recombination lifetime

Ecological validity of a simplified version of the multiple errands shopping test

Shallice and Burgess (1991) reported the utility of the Multiple Errands Test (MET) in discriminating executive deficits in three frontal lobe patients with preserved high IQ, who were otherwise unimpaired on tests of executive function. The aim of this study was to ascertain the value of a simplified version of the MET (MET-SV) for use with the range of people more routinely encountered in clinical practice. Main findings were as follows: 1) The test discriminated well between neurological patients and controls, and the group effects remained when the difference in current general cognitive functions (WAIS-R FSIQ) was taken into account. 2) The best predictors of performance in the healthy control group (n = 46) were age and the number of times participants asked for help (with more requests associated with poorer performance). 3) In the neurological group, two clear patterns of failure emerged, with performance either characterized by rule breaking or failure to achieve tasks. These two patterns were associated with different dysexecutive symptoms in everyday life. 4) The patients not only made more errors than controls, but also different ones. A scoring method that took this into account markedly increased test sensitivity. 5) Many patients passed traditional tests of executive frontal lobe function but still failed the MET-SV This pattern was strongly associated with observed dysexecutive symptoms in everyday life. The results demonstrate the clinical utility of the test, and suggest that there are two common and independent sources of failure on multitasking tests in a general neurological population: memory dysfunction, and initiation problems

The case for the development and use of "ecologically valid" measures of executive function in experimental and clinical neuropsychology

This article considers the scientific process whereby new and better clinical tests of executive function might be developed, and what form they might take. We argue that many of the traditional tests of executive function most commonly in use (e.g., the Wisconsin Card Sorting Test; Stroop) are adaptations of procedures that emerged almost coincidentally from conceptual and experimental frameworks far removed from those currently in favour, and that the prolongation of their use has been encouraged by a sustained period of concentration on “construct-driven” experimentation in neuropsychology. This resulted from the special theoretical demands made by the field of executive function, but was not a necessary consequence, and may not even have been a useful one. Whilst useful, these tests may not therefore be optimal for their purpose. We consider as an alternative approach a function-led development programme which in principle could yield tasks better suited to the concerns of the clinician because of the transparency afforded by increased “representativeness” and “generalisability.” We further argue that the requirement of such a programme to represent the interaction between the individual and situational context might also provide useful constraints for purely experimental investigations. We provide an example of such a programme with reference to the Multiple Errands and Six Element tests

High pressure polymorphism of ?-TaON

The high pressure behavior of TaON was studied using a combination of Raman scattering, synchrotron X-ray diffraction, and X-ray absorption spectroscopy in diamond anvil cells to 70 GPa at ambient temperature. A Birch–Murnaghan equation of state fit for baddeleyite structured ?-TaON indicates a high bulk modulus value Ko = 328 ± 4 GPa with K?o = 4.3. EXAFS analysis of the high pressure XAS data provides additional information on changes in the Ta–(O,N) and Ta–Ta distances. Changes in the X-ray diffraction patterns and Raman spectra indicate onset of a pressure induced phase transition near 33 GPa. Our analysis indicates that the new phase has an orthorhombic cotunnite-type structure but that the phase transition may not be complete even by 70 GPa. Similar sluggish transformation kinetics are observed for the isostructural ZrO2 phase. Analysis of compressibility data for the new cotunnite-type TaON phase indicate a very high bulk modulus Ko 370 GPa, close to the theoretically predicted value.<br/

The CROPGRO Perennial Forage Model Simulates Productivity and Re-Growth of Tropical Perennial Grasses

This paper introduces the CROPGRO Perennial Forage model (CROPGRO-PFM) and describes its ability to simulate regrowth dynamics and herbage production of Brachiaria and Panicum as affected by harvest management and weather. The model simulates regrowth, herbage harvests, percent leaf, and herbage protein of perennial forage grasses and legumes over multiple seasons. It can regrow from zero LAI (after harvest) based on use of carbohydrate and N reserves in storage tissues; however, the amount of residual stubble and residual leaf area index (LAI) are also important for rapid regrowth and productivity. The model is publically available for download from DSSAT.NET

Characterisation of the delamination process of nanoclays

Nanocomposites comprising delaminated nanoclays result in superior properties of the final product. This study aimed at monitoring the processes of intercalation and exfoliation of different nanoclay-polyol pairs performed through different dispersion protocols. X-ray diffraction, rheology and particle sizing are discussed in relation to the evolving product properties

Statin Therapy and Risk of Developing Type 2 Diabetes: A Meta-Analysis

OBJECTIVE: Although statin therapy reduces cardiovascular risk, its relationship with the development of diabetes is controversial. The first study (West of Scotland Coronary Prevention Study [WOSCOPS]) that evaluated this association reported a small protective effect but used nonstandardized criteria for diabetes diagnosis. However, results from subsequent hypothesis-testing trials have been inconsistent. The aim of this meta-analysis is to evaluate the possible effect of statin therapy on incident diabetes. RESEARCH DESIGN AND METHODS: A systematic literature search for randomized statin trials that reported data on diabetes through February 2009 was conducted using specific search terms. In addition to the hypothesis-generating data from WOSCOPS, hypothesis-testing data were available from the Heart Protection Study (HPS), the Long-Term Intervention with Pravastatin in Ischemic Disease (LIPID) Study, the Anglo-Scandinavian Cardiac Outcomes Trial (ASCOT), the Justification for the Use of Statins in Prevention: an Intervention Trial Evaluating Rosuvastatin (JUPITER), and the Controlled Rosuvastatin Multinational Study in Heart Failure (CORONA), together including 57,593 patients with mean follow-up of 3.9 years during which 2,082 incident diabetes cases accrued. Weighted averages were reported as risk ratios (RRs) with 95% CIs using a random-effects model. Statistical heterogeneity scores were assessed with the Q and I2 statistic.RESULTS In the meta-analysis of the hypothesis-testing trials, we observed a small increase in diabetes risk (RR 1.13 [95% CI 1.03–1.23]) with no evidence of heterogeneity across trials. However, this estimate was attenuated and no longer significant when the hypothesis-generating trial WOSCOPS was included (1.06 [0.93–1.25]) and also resulted in significant heterogeneity (Q 11.8 [5 d.f.], P = 0.03, I2 = 57.7%). CONCLUSIONS: Although statin therapy greatly lowers vascular risk, including among those with and at risk for diabetes, the relationship of statin therapy to incident diabetes remains uncertain. Future statin trials should be designed to formally address this issue

Tourism and toponymy: Commodifying and Consuming Place Names

Academic geographers have a long history of studying both tourism and place names, but have rarely made linkages between the two. Within critical toponymic studies there is increasing debate about the commodification of place names, but to date the role of tourism in this process has been almost completely overlooked. In some circumstances, toponyms can become tourist sights based on their extraordinary properties, their broader associations within popular culture, or their role as metanyms for some other aspect of a place. Place names may be sights in their own right or ‘markers’ of a sight and, in some cases, the marker may be more significant than the sight to which it refers. The appropriation of place names through tourism also includes the production and consumption of a broad range of souvenirs based on reproductions or replicas of the material signage that denote place names. Place names as attractions are also associated with a range of performances by tourists, and in some cases visiting a place name can be a significant expression of fandom. In some circumstances, place names can be embraced and promoted by tourism marketing strategies and are, in turn, drawn into broader circuits of the production and consumption of tourist space

Addressing Barriers to Housing in Reentry Programs Working to Address a Variety of Needs: A Qualitative Study of Second Chance Act Grantees

Using data from an evaluation of three Second Chance Act grantees, we explore formerly incarcerated people’s (FIP) access to housing. This study is unique in that it includes the perspectives of individuals with lived experiences and the insights of the reentry program providers working to meet their overall needs, including in the area of housing. The data come from reentry programs in three regions of the United States. Although the needs of the people with lived experiences have similarities, regional differences exist, particularly related to housing costs and supply, including the availability of transitional housing. Also, variations exist between FIP who are able to live with family compared with those who do not have this option. The three programs this study examined worked to address housing needs in distinctive ways and explores the housing needs of FIP and the strategies the three programs use to address these needs. Incorporating a two-pronged approach, this article includes analyses of (1) interview data with 31 FIP from 3 months to 3 years post-incarceration and (2) interviews and program materials to support formulative case analyses of the housing-related work that program enacted. Through this work, highlighting program efforts to remove barriers to housing for this population, the study seeks to promote the advancement of relevant policy, practice, and research in this arena

Prevalence and factors associated with potentially inappropriate medication and medication complexity for older adults in the emergency department of a secondary teaching hospital in Indonesia

Background: Older adults experience progressive decline in various organs and changes in pharmacokinetics and pharmacodynamics of the drugs in the body which lead to an increased risk of medication-related problems. Potentially inappropriate medications (PIMs) and medication complexity are key factors contributing to adverse drug events in the emergency department (ED). Objective: To estimate the prevalence and investigate the risk factors of PIMs and medication complexity among older adults admitted to the ED. Methods: A retrospective observational study was conducted among patients aged > 60 years admitted to the ED of Universitas Airlangga Teaching Hospital in January-June 2020. PIMs and medication complexity were measured using the 2019 American Geriatrics Society Beers Criteria® and Medication Regimen Complexity Index (MRCI), respectively. Results: A total of 1005 patients were included and 55.0% (95% confidence interval [CI]: 52 – 58%) of them received at least one PIM. Whereas, the pharmacological therapy prescribed to older adults had a high complexity index (mean MRCI 17.23 + 11.15). Multivariate analysis showed that those with polypharmacy (OR= 6.954; 95% CI: 4.617 – 10.476), diseases of the circulatory system (OR= 2.126; 95% CI: 1.166 – 3.876), endocrine, nutritional, and metabolic diseases (OR= 1.924; 95% CI: 1.087 – 3.405), and diseases of the digestive system (OR= 1.858; 95% CI: 1.214 – 2.842) had an increased risk of receiving PIM prescriptions. Meanwhile, disease of the respiratory system (OR = 7.621; 95% CI: 2.833 – 15.150), endocrine, nutritional and metabolic diseases (OR = 6.601; 95% CI: 2.935 – 14.847), and polypharmacy (OR = 4.373; 95% CI: 3.540 – 5.401) were associated with higher medication complexity. Conclusion: In our study, over one in every two older adults admitted to the ED had PIMs, and a high medication complexity was observed. Endocrine, nutritional and metabolic disease was the leading risk factors for receiving PIMs and high medication complexity