Magnetic resonance studies of point defects in single crystal diamond

The results from EPR studies of CVD diamond which was intentionally silicon doped with isotopes in natural abundance or isotopically enriched are reported. The observation of hyperfine satellites arising due to the presence of 29Si has provided definitive evidence for the involvement of silicon in two EPR centres in diamond which were previously suspected to involve silicon: KUL1 and KUL3. KUL1 is unambiguously identified as the neutral silicon split vacancy defect (V-Si-V)0, whilst KUL3 is shown to be (V-Si-V)0 decorated with a hydrogen atom. Data have also revealed that (V-Si-V)0 is preferentially oriented in samples grown on {110} substrates. The negative nitrogen-vacancy centre (NV‑) has been investigated. Published parameters for the nitrogen hyperfine interaction produce an unsatisfactory fit to the experimental spectra and hence these parameters are redetermined. Optically-excited EPR has been used to estimate the degree of spin polarisation of the NV-ground state and the increase in signal intensity with illumination has permitted the interaction between the unpaired electron and neighbouring 13C atoms to be studied. Two sets of 13C hyperfine satellites have been identified, which account for ~100% of the unpaired electron probability density. Despite the predictions that the neutral charge state of NV should have an S = ½ ground state, this charge state has not previously been detected by EPR. Optically excited EPR measurements reveal a trigonal nitrogen containing defect in diamond with an excited state populated via optical excitation. Analysis of the spin-Hamiltonian parameters and the wavelength dependence of the optical excitation leads to assignment of this state to the 4A2 excited state of NV0

Electrostatic Modulation of the Electronic Properties of Dirac Semimetal Na3Bi

Large-area thin films of topological Dirac semimetal Na$_3$Bi are grown on amorphous SiO$_2$:Si substrates to realise a field-effect transistor with the doped Si acting as back gate. As-grown films show charge carrier mobilities exceeding 7,000 cm$^2$/Vs and carrier densities below 3 $\times$10$^{18}$ cm$^{-3}$, comparable to the best thin-film Na$_3$Bi. An ambipolar field effect and minimum conductivity are observed, characteristic of Dirac electronic systems. The results are quantitatively understood within a model of disorder-induced charge inhomogeneity in topological Dirac semimetals. Due to the inverted band structure, the hole mobility is significantly larger than the electron mobility in Na$_3$Bi, and when present, these holes dominate the transport properties.Comment: 5 pages, 4 figures; minor corrections and revisions for readabilit

Cardiac autonomic and salivary responses to a repeated training bout in elite swimmers

This study examined the acute training responses of heart rate variability (HRV) and salivary biomarkers (immunoglobulin A and alpha-amylase) following a standardised training bout in Paralympic swimmers. Changes in HRV, sIgA and sAA were documented Monday morning, Monday afternoon and Tuesday morning over a 14-week monitoring period leading into international competition. Magnitude based inferences with effect sizes (ES) were used to assess the practical significance of changes each week. Normal training responses elicited increases in HR, 1, sAA and sIgA, accompanied by decreases in HF(nu), standard deviation of instantaneous RR variability (SD1) and the root mean square of successive differences (RMSSD) from Monday morning to Monday afternoon, and to Tuesday morning with similar week to week responses for most variables. Changes in RMSSD from Monday a.m. to p.m. were likely smaller (less negative) for Week 7 (78/18/3, ES = 0.40) following a competition weekend with similar changes observed from Monday a.m. to Tuesday a.m. (90/5/5, ES = 1.30). In contrast, the change in sAA from Monday a.m. to p.m. was very likely less (more negative) at Week 7 (0/0/99, ES = -2.46), with similar changes observed from Monday a.m. to Tuesday a.m. (0/0/99, ES = -4.69). During the taper period, there were also likely increases in parasympathetic modulations (RMSSD, Weeks 12-14) along with increased immune function (sIgA, Week 13) that demonstrated a favourable state of athlete preparedness. Used together, HRV and sAA provide coaches with valuable information regarding physiological changes in response to training and competition

Magnetic resonance studies of point defects in single crystal diamond

The results from EPR studies of CVD diamond which was intentionally silicon doped with isotopes in natural abundance or isotopically enriched are reported. The observation of hyperfine satellites arising due to the presence of 29Si has provided definitive evidence for the involvement of silicon in two EPR centres in diamond which were previously suspected to involve silicon: KUL1 and KUL3. KUL1 is unambiguously identified as the neutral silicon split vacancy defect (V-Si-V)0, whilst KUL3 is shown to be (V-Si-V)0 decorated with a hydrogen atom. Data have also revealed that (V-Si-V)0 is preferentially oriented in samples grown on {110} substrates. The negative nitrogen-vacancy centre (NV‑) has been investigated. Published parameters for the nitrogen hyperfine interaction produce an unsatisfactory fit to the experimental spectra and hence these parameters are redetermined. Optically-excited EPR has been used to estimate the degree of spin polarisation of the NV-ground state and the increase in signal intensity with illumination has permitted the interaction between the unpaired electron and neighbouring 13C atoms to be studied. Two sets of 13C hyperfine satellites have been identified, which account for ~100% of the unpaired electron probability density. Despite the predictions that the neutral charge state of NV should have an S = ½ ground state, this charge state has not previously been detected by EPR. Optically excited EPR measurements reveal a trigonal nitrogen containing defect in diamond with an excited state populated via optical excitation. Analysis of the spin-Hamiltonian parameters and the wavelength dependence of the optical excitation leads to assignment of this state to the 4A2 excited state of NV0.EThOS - Electronic Theses Online ServiceEngineering and Physical Sciences Research Council (Great Britain) (EPSRC)Diamond Trading Company Research Centre (Maidenhead) (DTCRC)GBUnited Kingdo

Studies of inspection algorithms and associated microprogrammable hardware implementations

This work is concerned with the design and development of real-time algorithms for industrial inspection applications. Rather than implement algorithms in dedicated hardware, microprogrammable machines were considered essential in order to maintain flexibility. After a survey of image pattern recognition where algorithms applicable to real-time use are cited, this thesis presents industrial inspection algorithms that locate and scrutinise actual manufactured products. These are fast and robust - a necessary requirement in industrial environments. The National Physical Laboratory have developed a Linear Array Processor (LAP) specifically designed for industrial recognition work. As with most array processors, the LAP has a greater performance than conventional processors, yet is strictly limited to parallel algorithms for optimum performance. It was therefore necessary to incorporate sequentialism into the design of a multiprocessor system. A microcoded bit-slice Sequential Image Processor (SIP) has been designed and built at RHBNC in conjunction with the NPL. This was primarily intended as a post-processor for the LAP based on the VMEbus but in fact has proved its usefulness as a stand-alone processor. This is described along with an assembler written for SIP which translates assembly language mnemonics to microcode. This work, which includes a review of current architectures, leads to the specification of a hybrid (SIMD/NIMD) architecture consisting of multiple autonomous sequential processors. This involves an analysis of various configurations and entails an investigation of the source of bottlenecks within each design. Such systems require a significant amount of interprocessor communication: methods for achieving this are discussed, some of which have only become practical with the decrease incost of electronic components. This eventually leads to a system for which algorithm execution speed increases approximately linearly with the number of processors. The algorithms described in earlier chapters are examined on the system and the practicalities of such a design are analysed in detail. Overall, this thesis has arrived at designs of programmable real-time inspection systems, and has obtained guidelines which will help with the implementation of future inspection systems.<p

How does drinking water affect attention and memory? The effect of mouth rinsing and mouth drying on children's performance

There is general consensus that drinking water facilitates certain cognitive processes. However, it is not yet known what mechanism underlies the effect of drinking on performance and these may be different for different cognitive processes. We sought to elucidate the mechanisms involved by establishing at what stage of the drinking process cognitive performance is influenced. We examined the effect of mouth rinsing and mouth drying on subjective thirst and mood, visual attention and short term memory in children. Data are reported from 24 children aged 9- to 10-years. Children's performance was assessed in three conditions - mouth drying, mouth rinsing and a control (no intervention). In each condition they were assessed twice - at baseline, before intervention, and 20 min later at test. Mouth rinsing improved visual attention performance, but not short term memory, mood or subjective thirst. The effects of mouth drying were more equivocal. The selective nature of the results is consistent with suggestions that different domains of cognition are influenced by different mechanisms

Low temperature transport on surface conducting diamond

Magneto-transport measurements were performed on surface conducting hydrogen-terminated diamond (100) hall bars at temperatures between 0.1-5 K in magnetic fields up to 8T.Comment: 2 pages Optoelectronic and Microelectronic Materials & Devices (COMMAD), 2012 Conferenc

Subjective thirst moderates changes in speed of responding associated with water consumption

Participants (N=34) undertook a CANTAB battery on two separate occasions after fasting and abstaining from fluid intake since the previous evening. On one occasion they were offered 500ml water shortly before testing, and on the other occasion no water was consumed prior to testing. Reaction times, as measured by Simple Reaction Time (SRT), were faster on the occasion on which they consumed water. Furthermore, subjective thirst was found to moderate the effect of water consumption on speed of responding. Response latencies in the SRT task were greater under the “no water” condition than under the “water” condition, but only for those participants with relatively high subjective thirst after abstaining from fluid intake overnight. For those participants with relatively low subjective thirst, latencies were unaffected by water consumption, and were similarly fast as those recorded for thirsty participants who had consumed water. These results reveal the novel finding that subjective thirst moderates the positive effect of fluid consumption on speed of responding. The results also showed evidence that practice also affected task performance. These results imply that, for speed of responding at least, the positive effects of water supplementation may result from an attenuation of the central processing resources consumed by the subjective sensation of thirst that otherwise impair the execution of speeded cognitive processes