The purpose of this investigation was to study the thermoelectric effects in a single crystal of antimony at liquid-helium temperatures.

The initial aim of this project was to improve the performance of a chromatographic bioreactor-separator (CBRS). In such a system, a dilute enzyme solution is pumped continuously through a preparative chromatographic column, while pulses of substrate are periodically injected on to the column. Enzymic reaction and separation are therefore performed in a single unit operation. The chromatographic columns used were jacketed glass columns ranging from 1 to 2 metres long with an internal diameter of 1.5 cm. Linking these columns allowed 1, 2, 3 and 4 metre long CBRS systems to be constructed. The hydrolysis of lactose in the presence of β~galactosidase was the reaction of study. From previous work at Aston University, there appeared to be no difficulties in achieving complete lactose hydrolysis in a CBRS. There did, however, appear to be scope for improving the separative performance, so this was adopted as an initial goal. Reducing the particle size of the stationary phase was identified as a way of achieving this improvement. A cation exchange resin was selected which had an average particle size of around half that previously used when studying this reaction. A CBRS system was developed which overcame the operational problems (such as high pressure drop development) associated with use of such a particle size. A significant improvement in separative power was achieved. This was shown by an increase in the number of theoretical plates (N) from about 500 to about 3000 for a 2 metre long CBRS, coupled with higher resolution. A simple experiment with the 1 metre column showed that combined bioreaction and separation was achievable in this system. Having improved the separative performance of the system, the factors affecting enzymic reaction in a CBRS were investigated; including pulse volume and the degree of mixing between enzyme and substrate. The progress of reaction in a CBRS was then studied. This information was related to the interaction of reaction and separation over the reaction zone. The effect of injecting a pulse over a length of time as in CBRS operation was simulated by fed batch experiments. These experiments were performed in parallel with normal batch experiments where the substrate is mixed almost instantly with the enzyme. The batch experiments enabled samples to be taken every minute and revealed that reaction is very rapid. The hydrodynamic characteristics of the two injector configurations used in CBRS construction were studied using Magnetic Resonance Imaging, combined with hydrodynamic calculations. During the optimisation studies, galactooligosaccharides (GOS) were detected as intermediates in the hydrolysis process. GOS are valuable products with potential and existing applications in food manufacture (as nutraceuticals), medicine and drug targeting. The focus of the research was therefore turned to GOS production. A means of controlling reaction to arrest break down of GOS was required. Raising temperature was identified as a possible means of achieving this within a CBRS. Studies were undertaken to optimise the yield of oligosaccharides, culminating in the design, construction and evaluation of a Dithermal Chromatographic Bioreactor-separator.

There is increasing public concern over the possible harmful effects of extra-low-frequency (ELF) electromagnetic (em) fields. A variety of harmful effects have been linked with em field exposure, for example depression and suicide, carcinogenesis, birth defects, and spontaneous abortion. The epidemiological evidence, especially the more recent studies, suggests that there may be a small increased risk of childhood cancers in those living near overhead power lines. However laboratory evidence to date does not support this link. An epidemiological correlation does not necessarily imply a causal relationship: to confirm such a relationship, biological and laboratory evidence is required. This work studies the magnitude of human exposure to ELF magnetic fields from overhead power lines and visual display units (VDUs) and also investigates possible health effects at the microscopic level through cell culture experiments. From the epidemiological evidence, an effect threshold of approximately 300 nT was estimated. Detailed magnetic field distributions were measured round a variety of visual display units and only a very few emitted magnetic fields even close to the 300 nT threshold. Following an in-depth case study of a VDU operator who suffered from a combination of symptoms including eyestrain and headaches, a study of the health of nearly 200 office workers and VDU users was set up. The aims of the study were to investigate the range and severity of symptoms suffered by VDU users, to investigate possible causes and to study response to VDU work at an individual level. It was found that those working between 10 and 30 hours per week at a VDU were more likely to suffer symptoms of ill health. In contrast, those working more than 30 hours per week at a VDU were not more likely to suffer symptoms when compared with a control group of those working less than 10 hours per week at a VDU. In particular, increased reporting of eye problems and fatigue were most strongly associated with VDU work.

Fast field-cycling MRI (FFC-MRI) is a novel technique that promises to expand upon the diagnostic capabilities of conventional MRI by allowing the main magnetic field, B0, to be varied during the imaging pulse sequence. By doing this it is possible to gain access to information that is hidden to conventional scanners - namely the variation of the spin-lattice relaxation time, T1, with field strength, known as T1 dispersion. However, adding B0 as a new dimension to the imaging process necessitates a longer scan time which can limit the techniques application to clinical research. In this thesis, several methods are explored for reducing FFC-MRI scan times. A rapid imaging pulse sequence based on the well-known Fast Spin-Echo imaging sequence is presented, as well as an adaptation of the “keyhole” acquisition strategy. A method of determining T1 which requires significantly less data - and hence scan time - is also presented. When combined, these techniques are demonstrated to reduce total scan time from several hours to minutes without compromising access to T1 dispersion information. The techniques are demonstrated in phantom studies and in vivo results from volunteers are presented as proof of concept. The reduction in scan time demonstrated by these methods will significantly improve the applicability of FFC-MRI for clinical trials which are currently being worked towards.

This thesis deals with the synthesis of dendritic gadolinium complexes based on DOTA, with a view to obtaining enhanced relaxivities. Li addition to the inherently long electronic relaxation time and high paramagnetic moment of the gadolinium (III) ion, the speed of rotation of its complexes in solution is a decisive parameter in the determination of the relaxivity. This parameter is dependent on the molecular mass of the complex. Initially, the enantioselective synthesis of novel a-substituted analogues of DOTA was attempted but was not successful due to difficulties encountered in attaining the tetraalkylation of cyclen and the purification of the products obtained. Therefore, further studies were carried out based on the known [Gd(gDOTA)]" system. The synthesis of three medium M(_W) dendrons, each with a focal primary amino group was carried out. Their structures may be described as dendrimeric analogues of poly(ethylene glycol). Two of these structures were successfully coupled to the gadolinium (III) chelate, [Gd.gDOTA]. The acid-catalysed epimerisation of the statistical distribution of stereoisomers yielded solely the (RRRR)/(SSSS) isomeric pair. This system had previously been shown to undergo fast water exchange. The coupling and deprotection procedure yielded paramagnetic dendritic complexes with molecular weights of 2013 and 3535.Relaxivity measurements were carried out on these systems and the results showed significantly higher relaxivities of 18 and 21 mM(^-1) s(^-1) respectively, compared with a value of 7.8 mM(^-1) s(^-1) for the parent compound. Examination of NMRD profiles for the larger system showed a decrease in the rotational correlation time to 310 ps at 298 K, as expected. However, this was accompanied by an increase in the inner-sphere water exchange lifetime to 570 ns at 298 K. Therefore, although an improvement in relaxivity was obtained through a coupling to the slower rotation of the system in solution, this enhancement was limited by the accompanying decrease in the rate of water exchange. The best fitting procedure of the NMRD profiling procedure revealed the presence of 8 second-sphere water molecules at an average distance of 4Å. The second sphere contribution was shown to be the dominant contributor to the overall relaxivity. This accounted for >50% of the increased relaxivity.

A thesis submitted to the faculty of science, University of the Witwatersrand, Johannesburg, In fulfilment of the requirements for the Degree of Doctor of Philosophy Johannesburg 1990 / The processing of near-earth satellite magnetometer data towards extracting an improved lithosphere anomaly map is addressed. The two aspects of the data reduction route where data quality has been compromised most by contemporary methods is researched, namely;[Abbreviated Abstract. Open document to view full version] / GR2017

稀磁半導體是通過摻雜磁性過渡金屬進入半導體基體而形成的。他們是一類部分磁性離子占居半導體本身離子態的新型半導體，擁有很多優異的特性，因而在工業和商業等方面具有廣泛的應用和巨大的潛能。磁性離子的出現使得他們擁有了有別于普通半導體材料的獨特磁性特性。室溫鐵磁性作爲特性之一已經在很多稀磁半導體中觀察到。然而，稀磁半導體中鐵磁序的來源一直備受爭議，因爲磁性摻雜劑本身擁有磁性性能。因此很難確定得到的産物確實是半導體與磁性過渡金屬摻雜劑的固溶體，還是半導體基包裹磁性過渡金屬團簇、沈析物或者二相，這些包裹的成分呈現了磁性特性。另外，絶大部分磁性過渡金屬在半導體基中溶解率都比較低。因此，人們越來越感興趣通過摻雜非過渡金屬摻雜劑來開發磁性系統。在這類系統中，可以排除鐵磁信號來源于摻雜劑，並且由于沒有鐵磁相互吸引力，可以實現較高的摻雜率。近來這樣的磁性系統已經被發展，例如碳摻雜的氧化鋅，碳摻雜的氧化钛等。 / 受這些想法的啓發，我們選擇非磁性元素鋁、鎢作爲摻雜劑，並將他們摻雜進入B₄C和SiC半導體基體中。利用高溫固相燒結法，以碳，硼和矽，鋁和鎢粉末作爲起始材料在2200ºC合成了鋁摻雜的B₄C，鋁摻雜的SiC和鎢摻雜的B₄C化合物。在鋁摻雜的B₄C體系中，鋁的摻雜沒有改變晶體結構。所有的摻雜樣品均保持與未摻雜樣品相同的晶體結構，即B₄C（ICDD-PDF：75-0424，空間群R-3m）。並且所有的結果，包括X射線衍射圖，拉曼譜，X射線光電子譜，都表明C-B-C鏈上的部分碳原子被摻雜的鋁原子所取代。替代導致這個系統中隨著鋁含量的增加而表現出鐵磁特性。更重要的是，在這個系統中觀察到了典型的自旋玻璃行爲。而在鋁摻雜的SiC系統中，所有的樣品，包括未摻雜樣品和摻雜樣品，都是包含了6H，4H和15R多型的混合物。相比之下，在這個系統中鐵磁序的變化與鋁摻雜的B₄C系統中的也有所不同。這表明在這兩種半導體中由于摻雜效應誘導的鐵磁序機制是不一樣的。爲了進一步的調查，嘗試以錳作爲摻雜劑。錳摻雜的SiC結果證實在SiC系統中鐵磁特征確實不依賴于摻雜劑。這兩個SiC系統證明了在摻雜的SiC系統中，鐵磁行爲與混合物中的一種SiC多型(15R-SiC)而非摻雜劑有關。鎢摻雜的B₄C是一個有趣的體系。 / 輕摻雜樣品呈現了鐵磁特性，但隨著鎢含量的增加鐵磁序減弱直至消失。在高摻雜的樣品中産生了B₂W₅二相，實驗證明它是沒有鐵磁性能的。作為比較，在相同燒結條件下合成了鎢和鋁共摻雜的B₄C。發現鋁和鎢各自發揮摻雜效應并促成共同的結果。一個虛弱的自旋玻璃特性在這個共摻雜的體系中被觀察到。 / 總之，四個不同的摻雜體系被合成。他們都表現出磁性特性的變化。其中鋁摻雜的B₄C體系還表現出自旋玻璃特性。這項工作證明非磁性摻雜劑確實能影響半導體的磁性特性，並促使摻雜的半導體表現出鐵磁性能。這使得這些摻雜的半導體表現的就像稀磁半導體材料一樣。這項工作提供了理想的系統來研究和闡明非過渡金屬摻雜的寬禁帶半導體中自旋序的來源問題。 / Diluted magnetic semiconductors (DMSs) are formed by doping magnetic transition metals (TMs) into semiconductor matrices. They are a type of new semiconductors with fraction of magnetic ions on the sites of semiconductor constituent ions. DMSs have some excellent properties which enhance their potentials for using in a wide range of industrial and commercial applications. The presence of substituted magnetic ions results in unique magnetic properties which distinguish them from the ordinary semiconductor materials. Room temperature ferromagnetic (FM) ordering，as one of the unique properties, has been observed in many DMSs. However, the origin of FM ordering in the DMSs is still controversial due to the presence of intrinsic magnetic properties possessed by the magnetic TM dopants. It is difficult to determinate whether the obtained products is indeed a solid solution of the semiconductor matrix and the magnetic TM dopant or it remains as semiconductor matrix engulfing a magnetic TM clusters, precipitates, or second phases that are responsible for the observed magnetic properties. Moreover, most of the magnetic TMs have extremely low solubility in the semiconductor matrix. Therefore, an increasing interest is provoked on developing magnetic systems by doping non-TM dopants. In this new type of system, the origin of the FM signal from the dopant can be eliminated, and higher doping ratio in the system can be expected due to no magnetic attraction. Recently, such magnetic systems have been obtained, for examples C-doped ZnO and C-doped TiO₂. / Inspired by these ideas, we had selected the non-magnetic element Al and W as the dopants, and introducing them to the semiconductor matrices, B₄C and SiC. The Al-doped B₄C, Al-doped SiC and W-doped B₄C compounds were synthesized by high temperature solid-state sintering of carbon, boron/silicon, and aluminum/tungsten powders at 2200ºC. In the Al-doped B₄C system, doping of Al had not altered the crystal structure. All of the doped samples retained the same structure as the un-doped sample, which corresponded to the B₄C (ICDD-PDF:75-0424, space group R-3m). All results, including results of XRD, Raman and XPS, indicated that the parts of the carbon atoms on the C-B-C chains were replaced by some of the doped Al atoms. The result of this replacement was that the system showed FM feature with increasing of the Al content. More important, a typical spin-glass behavior was observed in this system. While in the Al-doped SiC system, all of the samples, including un-doped and doped samples, were mixtures containing 6H-SiC, 4H-SiC and 15R-SiC polytype. By comparison, the changes in the FM ordering in this system were also different from those in the Al-B₄C system. This indicated that the induced mechanisms of FM ordering due to the doping effects on the two semiconductors were not the same. To further investigation, attempts were made by using Mn as dopants. The result of Mn-doped SiC confirmed that the FM feature in SiC systems indeed did not depend on with the dopants. The two doped SiC systems demonstrated that the FM behavior might be related to one type of SiC polytype (15R-SiC) in the mixture rather than dopants. / The W-doped B₄C system was an interesting one. The lightly doped sample showed FM feature, while the FM ordering became weak and disappeared with the increase of W content. A second phase B₂W₅ was produced in the highly doped samples. It was demonstrated that B₂W₅ had no FM feature. To compare, (W, Al) co-doped B₄C were also synthesized under the same heating condition. It was found that the doping effects of Al and of W played its own individual role, and facilitated a common outcome. A weak spin-glass feature was observed in the co-doped system but not in the W-doped system. / In summary, four systems were fabricated. All of them showed changes in magnetic behaviors. The Al-doped B₄C system showed spin-glass features for the first time. The results of this work demonstrated that the non-magnetic dopants indeed could affect the magnetic properties of semiconductors, and urged the doped-semiconductors to exhibit FM features. This made the doped-semiconductors behaved as DMS materials even there was no 3d electron in the whole of systems. This work provides an ideal system to illustrate the origin of spin order in non-TM doped wide-gap semiconductors. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Zhang, Caihong = 摻雜半導體中的誘導磁性特性 / 張彩虹. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references. / Abstracts also in Chinese. / Zhang, Caihong = Shan za ban dao ti zhong de you dao ci xing te xing / Zhang Caihong. / Abstract --- p.i / 摘要 --- p.iv / Acknowledgments --- p.vi / Table of contents --- p.vii / List of figure captions --- p.x / List of Table captions --- p.xiii / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Diluted magnetic semiconductors --- p.1 / Chapter 1.1.1 --- Origin --- p.1 / Chapter 1.1.2 --- Background --- p.2 / Chapter 1.1.3 --- Current development --- p.3 / Chapter 1.1.4 --- Present challenges --- p.5 / Chapter 1.2 --- Objectives of this work --- p.7 / References --- p.9 / Chapter Chapter 2 --- Magnetism and Semiconductors --- p.12 / Chapter 2.1 --- Magnetism --- p.12 / Chapter 2.1.1 --- Types of magnetism --- p.12 / Chapter 2.1.2 --- Spin glass --- p.15 / Chapter 2.1 --- B₄C --- p.18 / Chapter 2.2.1 --- Introduction --- p.18 / Chapter 2.2.2 --- Properties and applications --- p.19 / Chapter 2.2.3 --- Synthesis and phase diagram --- p.20 / Chapter 2.2.4 --- Structure and characterization --- p.21 / Chapter 2.2 --- SiC --- p.25 / Chapter 2.3.1 --- Properties and applications --- p.25 / Chapter 2.3.2 --- SiC polytypes --- p.26 / Chapter 2.3.3 --- SiC-base DMSs --- p.28 / References --- p.30 / Chapter Chapter 3 --- Methodology and Instrumentation --- p.34 / Chapter 3.1 --- Sample preparation --- p.34 / Chapter 3.2 --- Sample characterization --- p.36 / Chapter 3.3 --- Instrumentation --- p.37 / Chapter 3.3.1 --- High temperature furnace --- p.37 / Chapter 3.3.2 --- X-ray diffraction --- p.38 / Chapter 3.3.3 --- Raman spectroscopy --- p.39 / Chapter 3.3.4 --- X-ray photoelectron spectroscopy --- p.40 / Chapter 3.3.5 --- Scanning electron microscopy and Energy-dispersive X-Ray spectroscopy --- p.41 / Chapter 3.3.6 --- Transmission electron microscopy --- p.42 / Chapter 3.3.7 --- Physical properties measuring system --- p.43 / Chapter 3.3.7.1 --- Vibrating sample magnetometer --- p.43 / Chapter 3.3.7.2 --- AC measurement system --- p.44 / References --- p.46 / Chapter Chapter 4 --- Al-doped B₄C System --- p.47 / Chapter 4.1 --- Introduction --- p.47 / Chapter 4.2 --- Experiments --- p.48 / Chapter 4.3 --- Results and discussion --- p.49 / Chapter 4.3.1 --- Confirmation of the un-doped B₄C sample --- p.49 / Chapter 4.3.2 --- Confirmation of Al into the B₄C matrix --- p.51 / Chapter 4.3.3 --- Evaluation of magnetic properties --- p.59 / Chapter 4.3.4 --- Magnetism in the Al-B₄C --- p.62 / Chapter 4.4 --- Conclusions --- p.65 / References --- p.66 / Chapter Chapter 5 --- Al-Doped SiC System --- p.68 / Chapter 5.1 --- Introduction --- p.68 / Chapter 5.2 --- Experiment I --- p.69 / Chapter 5.2.1 --- Experimental condition 1 --- p.69 / Chapter 5.2.2 --- Results and discussion --- p.70 / Chapter 5.2.2.1 --- X-ray diffraction patterns --- p.70 / Chapter 5.2.2.2 --- Raman spectra --- p.72 / Chapter 5.2.2.3 --- Transmission electron microscopy images --- p.77 / Chapter 5.2.2.4 --- DC magnetization --- p.79 / Chapter 5.2.2.5 --- AC susceptibilities --- p.80 / Chapter 5.3 --- Experiment II --- p.81 / Chapter 5.3.1 --- Experimental condition 2 --- p.81 / Chapter 5.3.2 --- Results and discussion --- p.82 / Chapter 5.4 --- Experiment III --- p.88 / Chapter 5.4.1 --- Experimental condition 3 --- p.88 / Chapter 5.4.2 --- Results and discussion --- p.89 / Chapter 5.5 --- Mn-doped SiC --- p.91 / Chapter 5.5.1 --- Experimental condition --- p.91 / Chapter 5.5.2 --- Results and discussion --- p.92 / Chapter 5.6 --- Summary --- p.93 / Chapter 5.7 --- Conclusions --- p.94 / References --- p.95 / Chapter Chapter 6 --- W-doped and (W, Al)-codoped B₄C System --- p.98 / Chapter 6.1 --- Introduction --- p.98 / Chapter 6.2 --- Experiments --- p.99 / Chapter 6.3 --- Results and discussion --- p.101 / Chapter 6.3.1 --- X-ray diffraction patterns --- p.101 / Chapter 6.3.2 --- Raman spectra --- p.104 / Chapter 6.3.3 --- Scanning electron microscopy images --- p.106 / Chapter 6.3.4 --- DC magnetization --- p.108 / Chapter 6.3.5 --- AC susceptibilities --- p.111 / Chapter 6.4 --- Conclusions --- p.113 / References --- p.114 / Chapter Chapter 7 --- Summary and Suggestions for Future Work --- p.115 / Chapter 7.1 --- Summary --- p.115 / Chapter 7.2 --- Suggestions --- p.117 / References --- p.120

Thesis (M.Phil.)--Chinese University of Hong Kong. / Bibliography: leaves 100-103.

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