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Computer algebra removes much of the drudgery from mathematics; it allows users to formulate models by using the language of mathematics and to have those models evaluated with little effort. This symbolic form of representation is often thought of as being separate to dedicated computational programs such as Rietveld refinement. These dedicated programs are often written in low level languages; they are relatively inflexible in what they do and modifying them to change functionality in a small manner is often a major programming task. This paper describes a symbolic system that is integrated into the dedicated Rietveld refinement program called TOPAS. The symbolic component allows large functional changes to be made at run time and with a relatively small amount of effort. In addition, the system as a whole reduces the programming complexity at the developmental stage.
The Mineralogical Society of Great Britain & Ireland has published two full-colour posters describing the feldspar minerals, designed primarily for student use. They may be downloaded free of charge by all from http://www.minersoc.org/pages/education/edu.html and are designed to be printed at A3 size, although they are legible at A4 and in greyscale. Sheet 1 deals with nomenclature, crystal structure and phase relationships, while Sheet 2 covers phase behaviour. For brevity no sources are given on the posters, and these are provided in the present article, together with supporting notes and suggested reading on the more complex topics.
The Amigos de los Delfines made four sightings of humpback whales (Megaptera novaeangliae) during surveys for dolphins near the Parque Nacional del Este (Eastern National Park), on the south-eastern coast of the Dominican Republic in March 2005. A number of behaviours were documented, including breaching apparently in response to harassment by local tour boats. The northern waters of the country are well known breeding sites for humpback whales, which led to the creation of the Silver Bank Marine Mammal Sanctuary. The information obtained during these sightings has led to a number of management efforts to reduce the impacts of human activities on the whales beyond the borders of the Sanctuary.
The Assynt Culmination of the Moine Thrust Belt, in the northwest Scottish Highlands, contains a variety of Caledonian alkaline and calc-alkaline intrusions that are mostly of Silurian age. These include a significant but little-studied suite of dykes and sills, the Northwest Highlands Minor Intrusion Suite. We describe the structural relationships of these minor intrusions and suggest a classification into seven swarms. The majority of the minor intrusions can be shown to pre-date movement in the Moine Thrust Belt, but some appear to have been intruded during the period of thrusting. A complex history of magmatism is thus recorded within this part of the Moine Thrust Belt. New geochemical data provide evidence of a subduction-related component in the mantle source of the minor intrusions.
This issue of Mineralogical Magazine – Journal of Mineral Sciences contains nine articles by distinguished mineralogists which were delivered as plenary lectures to the 18th General Meeting of the International Mineralogical Association held in Edinburgh in early September 2002. The IMA is the only truly international organization representing mineralogy, and is supported by subscriptions from 37 mineralogical societies world-wide. Its main activity is to hold a General Meeting every four years in one of the subscribing countries, and in 2002 the organization was handled jointly by a group based in Edinburgh and by the Mineralogical Society of Great Britain & Ireland. The organizers invited lecturers who we believed would provide an authoritative and exciting overview of the most vigorous areas of the science of mineralogy as we enter a new millennium. In this the lecturers have unquestionably succeeded and we are very grateful for the scholarship, time and effort that they have put into these presentations. Each article was checked by an expert, and I thank Ross Angel, Derek Bain, Bill Brown, Martin Lee, David Manning, Bryne Ngwenya and Alison Pawley for their help.
Ovarian cancer is the commonest cause of death from gynaecological malignancy in the Western world. About 5000 new cases of this cancer are diagnosed each year in England and Wales (5% of all cancers), and it is the fourth commonest cancer in all women up to 85 years (after cancers of the breast, lung and large bowel). The life-time risk of developing ovarian cancer, in England and Wales, is 1 in 56, or 1.8% by the age of 85. Ovarian cancer incidence in England and Wales has increased gradually in the last two decades. Mortality rates are only slightly lower than the incidence rates – a reflection of its poor prognosis. In England and Wales, only 29% of women with the malignancy survive as long as five years after diagnosis although younger women do survive longer: 69% of those who are under 40 years old at diagnosis survive for five years compared to less than 20% for those aged 70 or more. Because of its high incidence and poor prognosis, ovarian cancer also represents the fourth most common cause of death from cancer among women in England and Wales, accounting for about 3600 deaths per year (7% of all cancer deaths).
Cortical spreading depression (CSD) and peri-infarct depolarisation (PID) are related phenomena that have been associated with the human clinical syndromes of migraine (CSD), head injury and stroke (PID). Nevertheless the existence of CSD in man remains controversial, despite the detection of this phenomenon in the brains of most, if not all, other animal species investigated. This failure to unambiguously detect CSD clinically may be at least partly due to the anatomically complex, gyrencephalic structure of the human brain. This study was designed to establish conditions for the study of CSD in the brain of a gyrencephalic species using the noninvasive technique of magnetic resonance imaging (MRI). The 3-dimensional (3D) gyrencephalic anatomy of the cat brain was examined to determine the imaging conditions necessary to detect CSD events. Orthogonal transverse, sagittal and horizontal T1-weighted image slices showed that the marginal and suprasylvian gyri were the most appropriate cortical structures to study CSD. This was in view of (1) their simple geometry: (2) their lengthy extent of grey matter orientated rostrocaudally in the cortex: (3) their separation by a sulcus across which CSD spread could be studied and (4) the discontinuity in the grey matter in these regions between the right and left hemispheres dorsal to the corpus callosum. The structure suggested by the T1-weighted images was corroborated by systematic diffusion tensor imaging to map the fractional anisotropy and diffusion trace. Thus a single horizontal image plane could visualise the neighbouring suprasylvian and marginal gyri of both cerebral hemispheres, whereas its complex shape and position ruled out the ectosylvian gyrus for CSD studies. With the horizontal imaging plane, CSD events were reproducibly detected by animating successive diffusion-weighted MR images following local KCl stimulation of the cortical surface. In single image frames, CSD detection and characterisation required image subtraction or statistical mapping methods that, nevertheless, yielded concordant results. In repeat experiments, CSD events were qualitatively similar in appearance whether elicited by sustained or transient KCl applications. Our experimental approach thus successfully describes cat brain anatomy in vivo, and elucidates the necessary conditions for the application of MRI methods to detect CSD propagation.
This article presents mechanisms for low temperature (<150°C) rf plasma enhanced chemical vapor deposition of silicon and silicon nitride thin films that lead to sufficient electronic quality for thin film transistor (TFT) fabrication and operation. For silicon deposition, hydrogen abstraction and etching, and silicon disproportionation reactions are identified that can lead to optimized hydrogen concentration and bonding environments at <150°C. Nitrogen dilution of SiH4/NH3 mixtures during silicon nitride deposition at low temperatures helps promote N-H bonding, leading to reduced charge trapping. Good quality amorphous silicon TFT's fabricated with a maximum processing temperature of 110°C are demonstrated on flexible transparent plastic substrates. Transistors formed with the same process on glass and plastic show linear mobilities of 0.33 and 0.12 cm2/Vs, respectively, with ION/IOFF ratios > 106.
We have developed new polarizing coating materials and processes which enable the fabrication of polarizers for large-area liquid-crystal displays. The polarizing materials are novel discotic surfactants which self-assemble in aqueous solutions to provide a stable liquid-crystalline phase within a wide range of concentrations and temperatures. These lyotropic liquid crystals in an aqueous medium can be spread on a substrate surface by a variety of techniques including a knife-like doctor blade, a rolling cylinder, or a roll-to-roll method. Under the shearing force applied during deposition, the liquid crystals align on the substrate forming a dichroic polarizer. This alignment process allows continuous production of large-area polarizing films at low cost compared with the current technology that requires stretching of the films. Thin coatings can be applied to flexible plastic films, glass, or rigid plastic substrates. Direct coating of the polarizing material on glass eliminates several process steps in liquid-crystal display production since lamination of the polarizing film is no longer required. These new polarizing films have a high optical performance including a polarizing efficiency of above 98% and a dichroic ratio as high as 7.7.
For the first time, we report a new poly-Si stepped gate Thin Film Transistor (SG TFT) on glass. The Density of States extracted from measured I-V characteristics has been used to evaluate the device performance with a two dimensional device simulator. The results show that the three-terminal SG TFT device has a switching speed comparable to a low voltage structure and the high on-current capability of a metal field plate (MFP) TFT and the potential for comparable breakdown characteristics.
A series of tetrahedrally bonded carbon (ta-C) films have been produced using a Filtered Cathodic Vacuum Arc System. The threshold field and current densities achievable have been investigated as a function of sp3/sp2 bonding ratio and nitrogen content. Typical undoped ta-C films have a threshold field of 15–20V/μm and optimally nitrogen doped films exhibit threshold fields as low as ∼ 5 V/μm. Current densities of typically 10-4 A/cm2 at an applied field of 20V/micron were also obtained.
Hydrogen elimination reactions, abstraction and etching, are monitored in real-time using a differentially pumped mass spectrometer, while intermittently exposing a hydrogenated silicon surface to atomic deuterium. The mass spectrometer signals are used to predict the kinetics of the abstraction reaction, and to qualitatively treat the etch reaction.
We present performance results of 4-inch full-color field emission display (FED) devices which are constructed by using Spindt type arrays with 80,000,000 Mo-metal tips, spacers, uniquely-developed low voltage color phosphors. Spindt type microtips with less than 1.1 urn in hole size are fabricated using a total internal reflection (TIR) holographic lithograpy method. Each color phosphor is electrophoretically deposited on the ITO line. The spacer which is screen-printed is characterized by a 3-dimentional surface analysis system. Electron emission pattern and luminance test of each pixel without cross talk are analyzed under different gate voltages. In addition, the total pressure and residual gas distributions inside the panel are investigated at various gap sizes between the cathode and anode plates.
Polycrystalline silicon (p-Si) TFT offers higher aperture ratio with integrated driver circuits compared to the conventional a-Si TFT in AM-LCD application. The advantages of the p-Si TFT as the pixel switching element will be more pronounced for AM-LCDs with large number of scan lines and/or high pixel density. This paper reviews challenges and issues associated with the technology of p-Si TFT, particularly in active silicon layer deposition, solid phase and laser crystallization, hydrogenation, leakage current, performance of different device architectures and reliability. Critical issues affecting the p-Si TFT AMLCD pixel design are analyzed, including: lithographic resolution and overlay accuracy, pixel density and aspect ratio, display format, storage to LC capacitance ratio, and gate dielectric thickness. Predictions on the regimes of dominance for different flat-panel technologies by advantages in performance and-or cost with respect to panel size and pixel density will be presented.
In situ mass spectroscopy is used to monitor and analyze the hydrogen elimination reaction products during cyclical exposure of thin films of amorphous silicon to a flux of atomic deuterium. Mass spectroscopy results that atomic deuterium etches deposited silicon forming SiD4 and abstracts hydrogen bonded to silicon in the film to form HD. The relative signal intensities show that abstraction is the primary hydrogen elimination mechanism. The energy of activation for the abstraction reaction is obtained from the mass spectroscopy signals through a first order kinetic analysis and is found to be approximately zero, indicating that abstraction is not thermally activated.