Given an integer matrix A, there is a unique matrix S of a particular form, called the Smith Normal Form, and non-unique unimodular matrices P and Q such that PAQ = S. It is often the case that these matrices P and Q will be used for further calculation, and as such it is desirable to find P and Q with small entries. In this thesis we address the problem of finding such P and Q with small entries, in particular in the case where A is a diagonal matrix, which arises as a final step in many published algorithms. Heuristic algorithms are developed which appear to do well in practice and some theory is developed to explain this behaviour. We also give an account of the implementation of an alternative algorithm which bypasses this intermediary diagonal form. The basic theoretical development of this is work by Storjohan.

Transitional cell carcinoma of the bladder is commonly encountered in urological practice. It affects people of a relatively young age causing economic and social distress to patients. In order to prevent the disease it is important to understand its pathogenesis. In this study, we have tumorigenically transformed a human urothelial cell by growing cells in a serum free, factor free, chemically defined culture. The tumorigenic property of the cell was determined by the generation of a tumor after inoculation into nude mouse. DNA fingerprinting analysis demonstrated the common back ground of the non-tumorigenic human urothelial cell and its tumorigenic transformant. This result also shows evidence of mutation occurring during transformation. By analysing conditioned medium, a significant reduction in the levels of soluble human stem cell factor and interleukin la were found in tumorigenic cell conditioned medium. A model derived from this evidence may suggest that tumor cells undergo further transformation under nutrient and growth factor deprived conditions. Intravesical chemotherapeutic agents in current use have shown moderate tumor-killing effects with some systemic or local side effects. Identification of a drug with better effect and less side effects is essential for the successful treatment of bladder tumors. Nitric oxide (NO) is a natural product of the human body with a role in tumor cell-killing. Thus by using NO as a chemotherapeutic agent we could at least expect limited side effects. Roussin's black salt (RBS) is a novel NO donor. Its cytotoxicity was tested on tumorigenic (T24) and non-tumorigenic (SV-HUC-1) human urothelial cells. The cytotoxicity of RBS was shown to be dose- and contact time- dependent. This cytotoxicity was enhanced by light irradiation and reduced in the presence of haemoglobin. The cytotoxic effect of RBS was also tested on CHO cells and the DNA repair deficient mutant xrs-5 cell line. Both colony forming and micronuclei forming assays demonstrated that xrs-5 cells are more sensitive to RBS than their counterpart. This result may indicate that NO is involved in the cytotoxicity of RBS and furthermore that DNA damage might be one possible mechanism by which the cytotoxic effect of RBS is expressed.

No description available.

Spectra were obtained from several sources for a fine abundance analysis of the extreme helium-rich star HD 168476. The atmospheric parameters are found using theoretical models and abundances determined for the ions identified in the spectra. The star is found to have an effective temperature of 14000°K, log(surface gravity) of 1.5 and a microturbulent velocity of 10 km/s. Over 1400 lines are identified on the spectra ranging in wavelength from 3100A to 4925A and 5490A to 6585A, and about 530 lines are suitable for the abundance analysis. It is confirmed that helium, carbon, nitrogen and neon are overabundant, with hydrogen and oxygen underabundant. An ultraviolet spectrum of the star is also obtained and lines identified. In addition to the ions found in the visible region of the spectrum, neutral ions are also present, indicating the possibility of a cool outer shell to the star. Photometric and spectroscopic observations are made to study the light and radial velocity of the star, to determine if it is variable. Statistical tests showed that the star is variable in its V magnitude, and most probably in its colours, as well as being variable in its radial velocity. No period is found and it is suspected that the variability may be complex. Several theories for the causes of the variability are discussed and a possible origin for the extreme helium-rich nature of the star mentioned.

The study examined the importance of (1) component parts, (2) view, (3) orientation and (4) size in the neural encoding of the sight of a complex object in the temporal cortex of the macaque. Studies focused on cells selectively responsive to the sight of the head/body but unresponsive to control stimuli. (1) Cells responsive to the static whole body were tested with two component parts of the body. 44% (29/66) of cells responded to the whole body and to one of the two body regions tested: 23 to the head; 6 to the body. 36% (24/66) responded independently to both regions of the body when tested in isolation. The remaining cells were selective for the entire body and unresponsive to component parts. Similar selectivity for component parts was observed amongst cells responsive to moving heads/bodies (18 cells tested). (2) 90% (66/73) of cells (selectively responsive to static or moving head/bodies) tested were sensitive to perspective view (viewer-centred). Comparable levels of view sensitivity were found for responses to the whole body and its parts. Contrary to some influential models of object recognition these results indicate view-specific processing for both the appearance of separate object components and for integration of information across components. (3) The majority of cells tested (18/25, 72%) were selectively responsive to a particular orientation in the picture plane of the static whole body stimulus. 7 cells generalised across all orientations (4 cell with pure generalisation; 3 cells with superimposed orientation tuning). Of all cells sensitive to orientation, the majority (15/21, 71%) were tuned to the upright image. (4) The majority of cells tested (81%, 13/16) were selective for a particular stimulus size. The remaining cells (3/16) showed generalisation across a 4 fold decrease in size from life-sized. Interestingly, all size sensitive cells were tuned to life-sized stimuli. These results do not support previous suggestions that cells responsive to the head and body are selective to the view but generalise across orientation and size. Here, extensive selectivity for size and orientation is reported. It is suggested that object part, view, orientation and size specific responses might be pooled to obtain generalising responses. Experience appears to affect neuronal coding in two ways: a) Cells become selective for multiple object components due to spatial and temporal association between parts; and b) more cells become tuned to views, orientations and image sizes commonly experienced.

The theme of this paper is the unification of two theories which arose and were developed independently of one another in the latter part of the 19th century and the beginning of the 20th, namely the theory of series expansion of rational integral functions of several sets of variables, homogeneous in the variables of each set, that is the series expansion of algebraic forms in several sets of variables, and the theory of induces linear transformations, or invariant matrices. I have divided the work into five chapters of which the first and third are purely historical; Chapter I is an account of various methods, devised before the introduction of the ideas of standard order and standard tableaux, of forming series expansions of algebraic forms, while Chapter III is mainly occupied by an account of Schnur's work on invariant matrices. Chapters II, IV and V establish the link between the two theories and, at the expense of one or two points of repetition of definitions, are self-contained and may be read consecutively, more or less without reference to the other two chapters.

Edward B. Roberts. / "November 1990". "This paper is based on materials contained in E.B. Roberts, Entrepreneurs and High-Technology, Lessons from M.I.T. and Beyond (New York: Oxford University Press, forthcoming 1991)." / Includes bibliographical references (p. 24-25).

Abbie Griffin, John R. Hauser. / "July 1990." / Includes bibliographical references (p. 14-16). / Research partially supported by an American Fellowship from the American Association for University Women, the Marketing Science Institute and the Industrial Research Institute.

Alan N. Afuah, James M. Utterback. / "July 1990". / Includes bibliographical references (p. 25-26).

Marc H. Meyer, James M. Utterback. / Includes bibliographical references (p. 22-24). / Supported by the Center for Innovation Management Studies at Lehigh University, the Leaders for Manufacturing Program at MIT, and the International Center for Research on the Management of Technology at the MIT Sloan School of Management.