Experimental evidence for the molecular molybdenum fluorides MoF to MoF6: a matrix isolation and DFT investigation

All of the molecular molybdenum fluorides, MoF to MoF6, have been synthesised from the reaction of thermally evaporated molybdenum atoms with fluorine molecules and atoms, trapped in argon matrices, and characterised by matrix isolation IR spectroscopy in conjunction with DFT calculations. This includes the first spectroscopic characterisation of MoF and MoF2, the latter of which is very bent with a bond angle of ca. 133°, the reassignment of the IR spectral data for trigonal planar MoF3, the observation of tetrahedral MoF4, the assignment of new features to MoF5 which displays a Jahn-Teller distorted trigonal bipyramidal structure, and octahedral MoF6. When the reaction of fluorine molecules and heated molybdenum is allowed to take place, MoF6, MoF4 and (MoF5)3 are observed

Developing undergraduate practical skills and independence with ‘at home practical kits’

The Covid-19 pandemic posed significant challenges for practical teaching within the sciences. While many instructors adopted innovative alternatives to conventional practicals, many relied on digital approaches that did not give students hands-on experience. In this study we evaluate the use of ‘at home’ practical kits used in first year physics and biology teaching at a UK university as an alternative to laboratory classes. In particular we focus on the enforced independence over time, space and help-seeking inherent in the at-home model as a driver of student learning and confidence. Students reported the kits encouraged independence, problem solving and self-reliance. Students associated the at-home practical kits with higher level cognitive skills as defined by Bloom’s revised taxonomy. While most students enjoyed using the kits, those who did not enjoy them tended to have higher previous experience of practical work before university. Students saw potential value in the kits after the pandemic, so could be an alternative or supplement to in-person practicals. We recommend that practical organisers use our findings around the development of student self-reliance to reconsider practical design and incorporate more opportunities for students to solve problems independently to increase effectiveness of practical teaching

Patients who choose not to dialyze: a prospective national observational study in Australia.

BACKGROUND: It is unclear how many incident patients with stage 5 chronic kidney disease (CKD) referred to nephrologists are presented with information about conservative care as a treatment option and how many plan not to dialyze. STUDY DESIGN: National observational survey study with random-effects logistic regression. SETTING & PARTICIPANTS: Incident adult and pediatric pre-emptive transplant, dialysis, and conservative-care patients from public and private renal units in Australia, July to September 2009. PREDICTORS: Age, sex, health insurance status, language, time known to nephrologist, timing of information, presence of caregiver, unit conservative care pathway, and size of unit. OUTCOMES & MEASUREMENTS: The 2 main outcome measures were information provision to incident patients about conservative care and initial treatment regardless of planned conservative care. RESULTS: 66 of 73 renal units (90%) participated. 10 (15%) had a formal conservative-care pathway. Of 721 incident patients with stage 5 CKD, 470 (65%) were presented with conservative care as a treatment option and 102 (14%) planned not to dialyze; median age was 80 years. Multivariate analysis for information provision showed that patients older than 65 years (OR, 3.40; 95% CI, 1.97-5.87) and those known to a nephrologist for more than 3 months (OR, 6.50; 95% CI, 3.18-13.30) were more likely to receive information about conservative care. Patients with conservative care as planned initial treatment were more likely to be older than 65 years (OR, 4.71; 95% CI, 1.77-12.49) and women (OR, 2.23; 95% CI, 1.23-4.02) than those who started dialysis therapy. Those with private health insurance were less likely to forgo dialysis therapy (OR, 0.40; 95% CI, 0.17-0.98). LIMITATIONS: Cross-sectional design prohibited longer term outcome measurement. Excluded patients with stage 5 CKD managed in the community. CONCLUSIONS: 1 in 7 patients with stage 5 CKD referred to nephrologists plans not to dialyze. Comprehensive service provision with integrated palliative care needs to be improved to meet the demands of the aging population

Patients who choose not to dialyze: a prospective national observational study in Australia.

BACKGROUND: It is unclear how many incident patients with stage 5 chronic kidney disease (CKD) referred to nephrologists are presented with information about conservative care as a treatment option and how many plan not to dialyze. STUDY DESIGN: National observational survey study with random-effects logistic regression. SETTING & PARTICIPANTS: Incident adult and pediatric pre-emptive transplant, dialysis, and conservative-care patients from public and private renal units in Australia, July to September 2009. PREDICTORS: Age, sex, health insurance status, language, time known to nephrologist, timing of information, presence of caregiver, unit conservative care pathway, and size of unit. OUTCOMES & MEASUREMENTS: The 2 main outcome measures were information provision to incident patients about conservative care and initial treatment regardless of planned conservative care. RESULTS: 66 of 73 renal units (90%) participated. 10 (15%) had a formal conservative-care pathway. Of 721 incident patients with stage 5 CKD, 470 (65%) were presented with conservative care as a treatment option and 102 (14%) planned not to dialyze; median age was 80 years. Multivariate analysis for information provision showed that patients older than 65 years (OR, 3.40; 95% CI, 1.97-5.87) and those known to a nephrologist for more than 3 months (OR, 6.50; 95% CI, 3.18-13.30) were more likely to receive information about conservative care. Patients with conservative care as planned initial treatment were more likely to be older than 65 years (OR, 4.71; 95% CI, 1.77-12.49) and women (OR, 2.23; 95% CI, 1.23-4.02) than those who started dialysis therapy. Those with private health insurance were less likely to forgo dialysis therapy (OR, 0.40; 95% CI, 0.17-0.98). LIMITATIONS: Cross-sectional design prohibited longer term outcome measurement. Excluded patients with stage 5 CKD managed in the community. CONCLUSIONS: 1 in 7 patients with stage 5 CKD referred to nephrologists plans not to dialyze. Comprehensive service provision with integrated palliative care needs to be improved to meet the demands of the aging population

The views of patients and carers in treatment decision making for chronic kidney disease: systematic review and thematic synthesis of qualitative studies

Objective To synthesise the views of patients and carers in decision making regarding treatment for chronic kidney disease, and to determine which factors influence those decisions

X-ray absorption study of platinum and palladium atoms in argon matrices: Evidence for platinum in a substitutional site and a short Pd–Ar interaction

The Pt L3-edge X-ray absorption spectrum of Pt atoms generated in a hollow cathode sputtering device and trapped in an Ar matrix yielded a PtAr distance of 3.78(4) Å with a coordination number of ca. 12 which confirms the evidence from electronic absorption spectroscopy that Pt atoms occupy a substitutional site in the Ar lattice. These data also yield a van der Waals radius for Pt atoms of 1.90 Å. The Pd K-edge X-ray absorption spectrum of sputtered Pd atoms trapped in an Ar matrix is radically different to that for Pt atoms. The analysis reveals a much shorter PdAr distance of 2.53(3) Å with a low coordination number close to 1, together with an “atomic” EXAFS like spectrum with no significant oscillations indicating the absence of any well defined nearest neighbours. On annealing to 25 K, the 2.53(3) Å interaction essentially disappears to leave the “atomic” spectrum. The featureless “atomic” spectrum is associated with Pd 1S0 atoms in an argon substitutional site, or other site such as a grain boundary with high disorder. The short PdAr distance of 2.53(3) Å is consistent with Pd atoms with a 1S0 atomic ground state in an interstitial octahedral site, the formation of a PdArn exciplex with a short PdAr distance, or the formation of a more formal palladium argon compound such as PdAr2. Although it is not possible to be definitive, the most likely carrier of the short PdAr distance is a PdArn exciplex. What is clear is that this work has identified a short PdAr interaction for the first time

Searching for Monomeric Nickel Tetrafluoride: Unravelling Infrared Matrix Isolation Spectra of Higher Nickel Fluorides

Binary transition metal fluorides are textbook examples combining complex electronic features with most fundamental molecular structures. High‐valent nickel fluorides are among the strongest known fluorinating and oxidizing agents, but there is a lack of experimental structural and spectroscopic investigations on molecular NiF3 or NiF4. Apart from their demanding synthesis, also their quantum‐chemical description is difficult due to their open shell nature and low‐lying excited electronic states. Distorted tetrahedral NiF4 (D2d) and trigonal planar NiF3 (D3h) molecules were produced by thermal evaporation and laser ablation of nickel atoms in a fluorine/noble gas mixture and spectroscopically identified by a joint matrix‐isolation and quantum‐chemical study. Their vibrational band positions provide detailed insights into their molecular structures

A simple photoacoustic method for the in situ study of soot distribution in flames

This paper presents a simple photoacoustic technique capable of quantifying soot volume fraction across a range of flame conditions. The output of a high-power (30 W) 808-nm cw-diode laser was modulated in order to generate an acoustic pressure wave via laser heating of soot within the flame. The generated pressure wave was detected using a micro-electro-mechanical microphone mounted close to a porous-plug flat-flame burner. Measurements were taken using the photoacoustic technique in flames of three different equivalence ratios and were compared to laser-induced incandescence. The results presented here show good agreement between the two techniques and show the potential of the photoacoustic method as a way to measure soot volume fraction profiles in this type of flame. We discuss the potential to implement this technique with much lower laser power than was used in the experiments presented here

Experimental and theoretical studies of surface and volume changes in dielectrics induced by long-pulse RF CO₂ laser irradiation

This thesis describes research into infrared (IR) laser irradiation and damage of four commercially significant polymers: polyimide (PI), polyether ether ketone (PEEK), polyethylene terephthalate (PET) and polypropylene (PP). Many research groups have studied the laser ablation and irradiation of polymers, but they have focussed mainly on ultraviolet and pulsed infrared sources. There appears to be little published data for laser irradiation of polymers with IR lasers operating with pulse durations in the range 50µs to 1ms. Laser coupling to polymers is strongly dependent on the absorption coefficient at the emission wavelength. These properties are widely known and used to inform experimental practice but the absorption coefficient used in the literature is usually that measured at room temperature and low power. In this way it does not truly represent typical experimental conditions. It is also commonly assumed that the laser wavelength is constant. In this work the laser wavelength has been determined as a function of time during a typical pulse for a radio frequency (RF) excited CO2 laser. It was found that the emission wavelength could move from as short as 10.53µm to as long as 10.63µm during a 200µs duration pulse. This alone was seen to affect the absorption cofficient of the polymers studied. The absorption coefficient as a function of polymer temperature was measured over all wavelengths. This allowed any changes in the optical coupling during laser heating to be inferred. The change in absorption coefficient as a function of temperature was determined as being -0.40cm-1K-1, 0.86cm-1K-1, 0.48cm-1K-1and 0.04cm-1K-1 for PI, PEEK, PET and PP respectively at a wavelength of 10.59µm. The threshold fluence for damage was determined as a function of the laser pulse duration. Damage included any permanent change to the polymer surface and in this way took into account decomposition and melting, as well as ablation. Together with the absorption coefficient data, this allowed the energy densities to be calculated. For PI and PEEK these were found to be 2.4kJ/cm3 and 1.9kJ/cm3 respectively and agreed with existing data. The threshold energy density was 0.1kJ/cm3 for PET and 0.2kJ/cm3 for PP. These results were smaller than those expected from the literature due to melting rather than ablation taking place. The threshold fluence for each polymer was found to be mostly independent of laser pulse duration over the range investigated. The small thermal diffusivity of the materials was thought to be the reason for this. Calculations using solutions to the heat diffusion equation and a rate limited thermal decomposition model were found to be consistent with the experimental results. Some initial calculations of the effect of including the temperature dependent absorption coefficient indicated that this does indeed affect the temperature profile during and after the laser pulse. It has been shown that the RF CO2 laser is suitable for polymer processing, particularly for applications where spot size and high resolution etching are not an issue. Laser marking, cutting and hole-drilling would be acceptable applications for this laser which offers more choice in terms of duty-cycle and pulse duration than the pulsed TEA CO2 alternatives. Quantification of the thermal and optical properties and the interaction between these two parameters could be extended to other polymers and it is expected that similar behaviours would be observed.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Development of environmental water monitors based on hydrostatic and flourescence detection techniques

The research for this thesis led to the development of two environmental detectors, whose function was to identify predetermined threshold levels of the analyte. The research centred onto two types of analyte; immiscible and dissolved, both occurring in water based locations. The first detector was developed to detect the accumulation of oil within an oil/water interceptor. Pollution from oil spillages is a major contaminate of water systems and the control of this potentially hazardous material has legal obligations. This liquid, which naturally separates from water, accumulates within the interceptor enclosure and can be removed once the quantity of oil reaches the desired level. However, the often unpredictable nature of oil leaks and spillages means that the accumulation of oil within an interceptor is an irregular occurrence. Interceptor detectors based upon electrical techniques already exist. This research specifically developed a detection system that operated without any electrical devices within the interceptor. The research explored several possible avenues, eventually pursuing a technique based upon pressure change, based on the density differential between water and oil. The final system was capable of identifying when the oil had reached a depth of 200 to 250 mm within the interceptor. The second detection system, a portable microfluidic fluorimeter, was intended for placement in locations for the direct analysis of water. Glutathione was chosen as a model analyte, associated with a sex pheromone and prior to the onset of spawning may be found in high concentrations. The system that has been developed is capable of selectively sensing glutathione to below 10 μM. However, the threshold concentration in the proximity of its release as a pheromone is greater than 100 μM and within this range the fluorimeter produced a linear response. The fluorimeter used an LED light source with a PMT detector. An analysis could be made every seven minutes, using 150 μL each of analyte and reagent for every cycle. Through assessment of a pre-made standard, the viability of the microfluidic system could be assured with regards to blockages or other malfunctions of the system.EThOS - Electronic Theses Online ServiceGBUnited Kingdo