Plasma Dynamics

Contains a report on a research project

Plasma Dynamics

Contains research objectives and reports on two research projects

Designing avionics for lasers & optoelectronics

Unlike imagery-based Earth observation (EO) which has become very widely and cheaply available, gravity sensing EO has not yet emerged from its fundamental science roots. The challenge therefore is to develop gravity sensing instruments that can replicate the success of widespread imagery based EO. There are three main gravity sensing mechanisms under investigation: laser ranging (e.g., GRACE-FO [1]); atom interferometers, which measure gravitation perturbations to the wavefunctions of individual atoms; and ‘relativistic geodesy’ which uses atomic clocks to measure the gravitational curvature of spacetime. All three of these measurement systems use stabilised lasers as their main enabling technology. However traditional laboratory laser systems struggle to meet the robustness, reliability, or low size, weight, and power (SWaP) requirements for use in space. A demonstrator was build that adapted telecommunications industry COTS components, and software radio FPGA/DSP techniques, to develop a new all-fibre space-qualified stabilised laser systems for geodesy that have equivalent performance to laboratory systems. This instrument was used to develop a 780 nm laser system that is stabilised to the Rubidium D2 line - the stabilised laser most commonly required by the quantum and atomic sensing field achieving sufficiently high laser performance for the laser system to be immediately useful for quantum applications (stability: 1-10 kHz, accuracy: 1 MHz); and in an ultra-compact package that has the potential to be used in space (1 litre, 0.5 kg, 10 W) [2]. This paper reports on the current student work that advances the instrument further towards a flight payload – and key avionics design considerations for future researchers. This takes lessons learnt from the ESA ESEO software radio payload in utilising ECSS design practices [3] to fabricate a robust and modular avionics back-end board that can operate with numerous front-end laser or opto-electronics configurations for different quantum applications. The new board consists of a single PCB containing circuitry for TT&C reporting of power supply and voltage conditioning, the current and temperature electronics needed to control a diode laser on orbit, interfaces for photo detectors and opto-electronics, and a high-speed analogue- to-digital conversion network centred around a FPGA. As an example, digital signal processing performed frequency-modulated spectroscopy on a warm Rubidium vapour using an all-fibre optical arrangement

Plasma Dynamics

Contains reports on two research projects.WADC Contract AF33(616)-3984Servomechanisms Research Laborator

The local adsorption structure of benzene on Si(001)-(2 × 1): a photoelectron diffraction investigation

Scanned-energy mode C 1s photoelectron diffraction has been used to investigate the local adsorption geometry of benzene on Si(001) at saturation coverage and room temperature. The results show that two different local bonding geometries coexist, namely the 'standard butterfly' (SB) and 'tilted bridge' (TB) forms, with a composition of 58 ± 29% of the SB species. Detailed structural parameter values are presented for both species including Si–C bond lengths. On the basis of published measurements of the rate of conversion of the SB to the TB form on this surface, we estimate that the timescale of our experiment is sufficient for achieving equilibrium, and in this case our results indicate that the difference in the Gibbs free energy of adsorption, ΔG(TB)−ΔG(SB), is in the range −0.023 to +0.049 eV. We suggest, however, that the relative concentration of the two species may also be influenced by a combination of steric effects influencing the kinetics, and a sensitivity of the adsorption energies of the adsorbed SB and TB forms to the nature of the surrounding benzene molecules

Environmental impact of cadmium: a review by the Panel on Hazardous Trace Substances.

This report is the result of a review by a Panel on Hazardous Trace Substances, as part of a report to an ad hoc Committee on Environmental Health Research whose chairman was Dr. David Rall, Director of the National Institute of Environmental Health Sciences, NIH

Can the envisaged reductions of fossil fuel CO2 emissions be detected by atmospheric observations?

The lower troposphere is an excellent receptacle, which integrates anthropogenic greenhouse gases emissions over large areas. Therefore, atmospheric concentration observations over populated regions would provide the ultimate proof if sustained emissions changes have occurred. The most important anthropogenic greenhouse gas, carbon dioxide (CO2), also shows large natural concentration variations, which need to be disentangled from anthropogenic signals to assess changes in associated emissions. This is in principle possible for the fossil fuel CO2 component (FFCO2) by high-precision radiocarbon (14C) analyses because FFCO2 is free of radiocarbon. Long-term observations of 14CO2 conducted at two sites in south-western Germany do not yet reveal any significant trends in the regional fossil fuel CO2 component. We rather observe strong inter-annual variations, which are largely imprinted by changes of atmospheric transport as supported by dedicated transport model simulations of fossil fuel CO2. In this paper, we show that, depending on the remoteness of the site, changes of about 7–26% in fossil fuel emissions in respective catchment areas could be detected with confidence by high-precision atmospheric 14CO2 measurements when comparing 5-year averages if these inter-annual variations were taken into account. This perspective constitutes the urgently needed tool for validation of fossil fuel CO2 emissions changes in the framework of the Kyoto protocol and successive climate initiatives

Μulti-institutional dosimetric delivery assessment of intracranial stereotactic radiosurgery on different treatment platforms

BACKGROUND AND PURPOSE: Assessment of dosimetric accuracy of radiosurgery on different treatment platforms. MATERIAL AND METHODS: Thirty-three single fraction treatment plans were assessed at thirty centres using an anthropomorphic head phantom with target and brainstem structures. The target being a single irregular shaped target, ∼8cc, 10 mm from the brainstem. The phantom was "immobilised", scanned, planned and treated following the local protocols. EBT-XD films and alanine pellets were used to measure absolute dose, inside both the target and the brainstem, and compared with TPS predicted dose distributions. RESULTS: PTV alanine measurements from gantry-based linacs showed a median percentage difference to the TPS of 0.65%. Cyberknife (CK) had the highest median difference of 2.3% in comparison to the other platforms. GammaKnife (GK) showed the smallest median of 0.3%. Similar trends were observed in the OAR with alanine measurements showing median percentage differences of1.1%, 2.0% and 0.4%, for gantry-based linacs, CK and GK respectively. All platforms showed comparable gamma passing rates between axial and sagittal films. CONCLUSIONS: This comparison has highlighted the dosimetric variation between measured and TPS calculated dose for each delivery platforms.. The results suggest that clinically acceptable agreement with the predicted dose distributions is achievable by all treatment delivery systems. Radiosurgery, Dosimetry, End-to-end, Audit, Anthropomorphic Phantom, Alanine, Radiochromic film

Diurnal, seasonal, and annual trends in tropospheric CO in Southwest London during 2000–2015: Wind sector analysis and comparisons with urban and remote sites

Ambient carbon monoxide (CO) and meteorological parameters measured at the Egham (EGH) semi-rural site in SW London during 2000–2015 have permitted wind sector analysis of diurnal and seasonal cycles, and interpretation of long-term trends. CO daily amplitudes are used as a proxy for anthropogenic emissions. At EGH, morning and evening peaks in CO arise from the dominant contribution of road transport sources. Smaller amplitudes are observed during weekends than weekdays due to lower combustion emissions, and for mornings compared to evenings due to the timing of the development and break-up of the nocturnal inversion layer or planetary boundary layer (PBL). A wavelet transform revealed that the dominant mode of CO variability is the annual cycle, with apparent winter maxima likely due to increased CO emissions from domestic heating with summer minima ascribed to enhanced dispersion and dilution during the annual maximum of PBL mixing heights. Over the last two decades, both mitigation measures to reduce CO emissions and also a major switch to diesel cars, have accompanied a change at EGH from the dominance of local diurnal sources to a site measuring close to Atlantic background levels in summer months. CO observed in the S and SW wind sectors has declined by 4.7 and 5.9 ppb yr−1 respectively. The EGH CO record shows the highest levels in the early 2000s, with levels in E and calm winds comparable to those recorded at background stations in Greater London. However, since 2012, levels in S-SW sector have become more comparable with Mace Head background except during rush-hour periods. Marked declines in CO are observed during 2000–2008 for the NE, E, SE (London) and calm wind sectors, with the smallest declines observed for the S, SW and W (background) sectors. For the majority of wind sectors, the decline in CO is less noticeable since 2008, with an apparent stabilisation for NE, E and SE after 2009. The EGH CO data record exhibits a similar but slower exponential decay, but from a much lower starting concentration, than do CO data recorded at selected monitoring sites in urban areas in SE England. CO/CO2 residuals determined using a 1 h window data in the diurnal cycle demonstrate a clear decline in CO from 2000 to 2015 during daily periods of increased vehicle traffic, which is consistent with a sustained reduction in CO emissions from the road transport sector