The use of magnetic fields to create high-speed plasma jets for spacecraft propulsion

The aim of the work reported in this thesis has been to explore arrangements of magnetic fields and electric currents to create novel plasma thrusters that are more efficient and less complex than existing designs. Two original devices are discussed, firstly a thruster that uses a magnetic nozzle in combination with a High Power Impulse Magnetron Sputtering source (HiPIMS) to produce a jet of copper plasma and secondly, a thruster that uses the phenomena of magnetic reconnection that occurs between opposing magnetic fields in a plasma to produce a plasma jet. While HiPIMS has been normally employed to create thin films, the use of a solenoidal magnetic field to accelerate and focus the ions produced by that source has not been previously investigated as a means of creating a thruster. The HiPIMS thruster has a specific impulse (Isp) of 1543s. Magnetic reconnection has been studied for decades by geophysicists and by astronomers. Despite that effort, so far there has been little interest in exploiting the phenomena as a means of producing high-speed plasmas in a thruster despite the evidence of jets in those environments. A thruster consisting of two slit coaxial tubes of copper was constructed. Evidence for the occurrence of magnetic connection was fourfold. (1) A significant electron current that coincided with the rise of the magnetic field that was followed by a large ion current. (2) Ion currents were found to increase as the plasma became less collisional. (3) Ions with energies greater than 130 eV corresponding to a speed of 2.50 x 104 m/s and an Isp of 2550s were detected. (4) The ratio between the estimated speed of ions flowing into the diffusion layer (350m/s) and the measured speed of the out-flowing ions (2.50 x 104 m/s) was approximately 68. The physics indicates that such a thruster could have a basic energy efficiency of 50%

Not seeing the carbon for the trees? Why area-based targets for establishing new woodlands can limit or underplay their climate change mitigation benefits

Acknowledgements: The James Hutton Institute is supported by the Scottish Government’s Rural and Environment Science and Analytical Services Division (RESAS). This research was funded through both ClimatexChange and two strategic Research Programs (2011-16 and 2016-21). The authors acknowledge the assistance provided by other staff – Marie Castellazzi, Nikki Baggaley, Allan Lilly (The James Hutton Institute); Jo Smith (University of Aberdeen); Philip Taylor, Duncan Ray (Forest Research).Peer reviewedPublisher PD

Simulating impacts on UK air quality from net-zero forest planting scenarios

The UK proposes additional bioenergy plantations and afforestation as part of measures to meet net-zero greenhouse gas emissions, but species and locations are not yet decided. Different tree species emit varying amounts of isoprene and monoterpene volatile organic compounds that are precursors to ozone and secondary organic aerosol (SOA) formation, the latter of which is a component of PM2.5. The forest canopy also acts as a depositional sink for air pollutants. All these processes are meteorologically influenced. We present here a first step at coupling information on tree species planting suitability and other planting constraints with data on UK-specific BVOC emission rates and tree canopy data to simulate via the WRF-EMEP4UK high spatial resolution atmospheric chemistry transport model the impact on UK air quality of four potential scenarios. Our ‘maximum planting’ scenarios are based on planting areas where yields are predicted to be ≥50 % of the maximum from the Ecological Site Classification Decision Support System (ESC-DSS) for Eucalyptus gunnii, hybrid aspen (Populus tremula), Italian alder (Alnus cordata) and Sitka spruce (Picea sitchensis). The additional areas of forest in our scenarios are 2.0 to 2.7 times current suggestions for new bioenergy and afforestation landcover in the UK. Our planting scenarios increase UK annual mean surface ozone concentrations by 1.0 ppb or 3 % relative to the baseline landcover for the highest BVOC emitting species (e.g., E. gunni). Increases in ozone reach 2 ppb in summer when BVOC emissions are greatest. In contrast, all the additional planting scenarios lead to reductions in UK annual mean PM2.5 – ranging from -0.2 µg m-3 (-3 %) for Sitka spruce to -0.5 µg m-3 (-7 %) for aspen – revealing that PM2.5 deposition to the additional forest canopy area more than offsets additional SOA formation. Relative decreases in annual mean PM2.5 are greater than the relative increases in annual mean ozone. Reductions in PM2.5 are least in summer, coinciding with the period of maximum monoterpene emissions. Although only a first step in evaluating the impact of increased forest plantation on UK air quality, our study demonstrates the need for locally relevant data on landcover suitability, emissions and meteorology in model simulations

Competing risk bias in prognostic models predicting hepatocellular carcinoma occurrence: impact on clinical decision making

Existing models predicting hepatocellular carcinoma (HCC) occurrence do not account for competing risk events and, thus, may overestimate the probability of HCC. Our goal was to quantify this bias for patients with cirrhosis and cured hepatitis C. We analyzed a nationwide cohort of patients with cirrhosis and cured hepatitis C infection from Scotland. Two HCC prognostic models were developed: (1) a Cox regression model ignoring competing risk events and (2) a Fine-Gray regression model accounting for non-HCC mortality as a competing risk. Both models included the same set of prognostic factors used by previously developed HCC prognostic models. Two predictions were calculated for each patient: first, the 3-year probability of HCC predicted by model 1 and second, the 3-year probability of HCC predicted by model 2. The study population comprised 1629 patients with cirrhosis and cured HCV, followed for 3.8 years on average. A total of 82 incident HCC events and 159 competing risk events (ie, non-HCC deaths) were observed. The mean predicted 3-year probability of HCC was 3.37% for model 1 (Cox) and 3.24% for model 2 (Fine-Gray). For most patients (76%), the difference in the 3-year probability of HCC predicted by model 1 and model 2 was minimal (ie, within 0 to ±0.3%). A total of 2.6% of patients had a large discrepancy exceeding 2%; however, these were all patients with a 3-year probability exceeding >5% in both models. Prognostic models that ignore competing risks do overestimate the future probability of developing HCC. However, the degree of overestimation—and the way it is patterned—means that the impact on HCC screening decisions is likely to be modest

The risk of hepatocellular carcinoma in cirrhotic patients with hepatitis C and sustained viral response:role of the treatment regimen

Background & Aims: Previous studies have reported a high frequency of hepatocellular carcinoma (HCC) occurrence in patients with advanced liver disease, after receipt of interferon (IFN)-free therapy for hepatitis C virus (HCV) infection. Our objective was to verify and account for this phenomenon using data from the Scottish HCV clinical database. Methods: We identified HCC-naïve individuals with liver cirrhosis receiving a course of antiviral therapy in Scotland from 1997–2016 resulting in a sustained virologic response. Patients were followed-up from their treatment start date to the earliest of: date of death, date of HCC occurrence, or 31 January 2017. We used Cox regression to compare the risk of HCC occurrence according to treatment regimen after adjusting for relevant co-factors (including: demographic factors; baseline liver disease stage; comorbidities/health behaviours, virology, and previous treatment experience). HCC occurrence was ascertained through both the HCV clinical database and medical chart review. For our main analysis, treatment regimen was defined as IFN-free vs. IFN-containing. Results: A total of 857 patients met the study criteria, of whom 31.7% received an IFN-free regimen. Individuals receiving IFN-free therapy were more likely to be: older; of white ethnicity, Child-Turcotte-Pugh B/C vs. Child-Turcotte-Pugh A; thrombocytopenic; non-genotype 3; and treatment experienced. HCC occurrence was observed in 46 individuals during follow-up. In univariate analysis, IFN-free therapy was associated with a significantly increased risk of HCC (HR: 2.48; p = 0.021). However, after multivariate adjustment for baseline factors, no significant risk attributable to IFN-free therapy persisted (aHR: 1.15, p = 0.744). Conclusion: These findings suggest that the higher incidence of HCC following sustained virologic response with IFN-free therapy relates to baseline risk factors/patient selection, and not the use of IFN-free therapy per se. Lay summary: We examined the risk of liver cancer in 857 patients with cirrhosis in Scotland who received hepatitis C antiviral therapy and achieved a cure. We compared the risk of first-time liver cancer in patients treated with the newest interferon-free regimens, to patients treated with interferon. After accounting for the different characteristics of these two treatment groups, we found no evidence that interferon-free therapy is associated with a higher risk of liver cancer