[en] Strange particle production is one of the most useful probes of matter under extreme conditions of temperature and density. Due to the differences between quark masses in a Quark Gluon Plasma and hadron masses in a hadron gas scenario, there is a significant difference in the equilibration times for strange quark production under these two mechanisms. This difference in equilibration times will manifest itself in a much greater yield of strange particles from a QGP with respect to a hadron gas. It is believed that collisions of heavy ions at high energy may provide sufficient conditions for a QGP to be formed. The aim of the WA97 experiment is, therefore, to investigate relativistic heavy ion collisions at the CERN OMEGA Spectrometer, following on from the work of the WA85 and WA94 collaborations. Using a lead ion beam from the CERN Super Proton Synchrotron and a lead target, data were taken in both 1995 and 1996. As a control, in the autumn of 1995, data were also taken using a proton beam incident on a lead target. In 1996 the control was changed to a proton beam incident on a beryllium target. Significant enhancements in strange particle yields had already been seen when going from the p-Pb data to the Pb-Pb data. However, the lack of symmetry in the p-Pb collisions could, in theory, give misleading results and so analysis of the more symmetric p-Be data was needed in order to confirm these enhancements. The analysis of the data from the 1996 proton-beryllium run therefore forms the basis of this thesis. By observing the weak decays of the strange Λ, Λ-bar, Ξ^-, Ξ-bar⁺, Ω^- and Ω-bar⁺ hyperons, the yields per interaction and transverse mass spectra can be determined. The results from the p-Be data are then compared with the results for the p-Pb and Pb-Pb data. The inverse slope parameters from the transverse mass distributions give an indication of the temperature reached in the collisions, and a clear increase can be seen in this quantity as the size of the collision system increases. Yields are studied as a function of the number of nucleons participating in the collision, N_part, which is estimated using the Glauber model for the Pb-Pb data, and by averaging over impact parameter for the proton beam data. From the proton data to the Pb-Pb data, the yields per participant increase substantially. The enhancement is in agreement with QGP theory, in that it becomes more pronounced with the strangeness content of the particle, and exceeds an order of magnitude for the Ω. (author)

[en] The undoped parent compounds of high-temperature cuprate superconductors are known to be antiferromagnetic Mott insulators. As the CuO(sub 2) planes are doped with charge carriers, the antiferromagnetic phase subsides and superconductivity emerges. The symmetry, or the lack thereof, between doping with electrons (n-type) or holes (p-type) has important theoretical implications as most models implicitly assume symmetry. However, most of what we know about these superconductors comes from experiments performed on p-type materials. The much fewer number of measurements from n-type compounds suggest that there may be both commonalities and differences between the two sides of the phase diagram. This issue of electron/hole symmetry has not been seriously discussed, perhaps, because the experimental database of n-type results is very limited

[en] The Bernal liquid drop alpha particle model of a heavy nucleus shows (hat the fifth layer of alpha particles is not closed and is inherently unstable so mat the nucleus gradually decays by radiating alpha and beta particles until most of the fifth layer has been shed. It will be shown how alpha decay may be construed as the release of repulsive Coulomb energy that breaks six meson bonds and imparts kinetic energy to the alpha particle. In this way the alpha particle 'tunnels' through the Coulomb barrier. By contrast, in beta decay energy is released when a neutron decays into a proton and electron at the same time as four new meson bonds are formed. Together these two sources of energy balance the additional repulsive Coulomb energy generated by the new proton in the daughter nucleus and impart kinetic energy to the beta particle and anti-neutrino

[en] The Coulomb barrier to nuclear fusion is sometimes described as a barrier to nuclear fission. In this paper it will be shown that it is more meaningful to describe the repulsive Coulomb force between the daughters of fission as the cause of fission rather than a barrier. In fact it is this force which breaks the meson bonds between the daughters and imparts kinetic energy to them. This process may therefore be described as a quantum jump rather than a 'tunneling'. The Bemal liquid drop layered alpha particle model of a heavy nucleus shows that the sixth layer of alpha particles is not closed and is inherently unstable. This nucleus therefore either gradually decays by radiating alpha and beta particles until most of the sixth layer has been shed or it undergoes spontaneous fission to form a heavy daughter rarely containing less than four closed layers and a lighter daughter never containing less than three closed layers. It will be shown how each alpha decay involves the breaking of five or six meson bonds and each spontaneous fission breaks about thirty bonds

[en] Super-heavy nuclei are those transuranic nuclei with more than 106 protons . The underlying nuclear structure of super-heavy elements may be visualized as 5 concentric closed layers of alpha particles. This structure is an extension of layered alpha particle models of common nuclei based on Bernal's model of a drop of a monatomic liquid. It will be shown mat all super-heavy nuclei with atomic numbers in excess of 107 may be thought of as having a fifth closed layer of 16 alpha particles which decays because of its inherent instability

[en] By using the liquid drop model of 14 alpha particles representing a nickel 56 nuclide it can be shown that the mean distance of each of the 1d and 2s nucleons is r3 = 2.85 fm from the nuclide centre. It was found that the velocity of all nucleons is the same and is independent of the energy level. This implies that the de Broglie wavelength (w) of all nucleons is w h / m v = 6.3 fm ∼ 2π fm . Therefore for r1 ∼ 1 fm there is one w per orbit; for r2 ∼ 2 fm there are 2 w per orbit and so on. This implies that in the first magic number closed shell of nucleons there are 2 orbits each containing 2 standing wave maxima representing 1 proton and 1 neutron. The second closed shell consists of 3 orbits each containing 2 proton and 2 neutron standing wave maxima. While the third closed shell consists of 4 orbits each containing 3 protons and 3 neutrons the fourth closed shell consists of only 2 orbits each containing 4 protons and 4 neutrons. The Bernal liquid drop alpha particle models of nuclear structure appear to accord quite well with the quantum mechanical prescriptions of nucleon angular momentum and de Broglie wavelength

[en] Full text: Super-heavy nuclei are those transuranic nuclei with more than 106 protons. The lighter transuranic nuclei were first artificially synthesized during the 1940s and 50s by using cyclotrons to fuse either fast neutrons, hydrogen or helium nuclei with heavy target nuclei. The heavier transuranic nuclei were first produced in the 50s, 60s and 70s by accelerating boron, carbon, nitrogen or oxygen nuclei with linear accelerators to fuse with curium or californium targets. Since 1981 super-heavy nuclei containing up to 112 protons have been created by fusing chromium, iron, nickel or zinc with lead or bismuth. Recently nuclei with 114 protons have been fused from calcium and plutonium. The underlying nuclear structure of super-heavy elements may be visualized as 5 concentric layers of alpha particles. This structure is an extension of layered alpha particle models of common nuclei based on Bernal's model of a drop of a monatomic liquid in which hard spheres representing atoms are densely packed. This model successfully explained many properties of such liquids as well as those of metallic glasses. Norman showed how Bernal's model may be used to account for the size, density, quadrupole moment and binding energy levels of many nuclei if the hard spheres are alpha particles. Accordingly, an oxygen 16 nucleus is modeled as a single tetrahedral layer of 4 alpha particles. A second layer of 10 alpha particles models nickel 56; a third closed layer of 12 alphas forms the core of all nuclei containing at least 52 protons, and a fourth layer of 12 additional alphas forms a basis for those nuclei with 76 or more protons. Norman has also shown that this latter structure of 38 alphas constitutes the stable end point of the radioactive decay of heavy nuclei such as uranium. Furthermore, when a uranium nucleus undergoes fission induced by thermal neutrons it forms a light fragment with a core of no less than 2 alpha layers and a heavier daughter with a core of rarely less than 3 alpha layers. It will be shown that all super-heavy nuclei with atomic numbers in excess of 107 may be thought of as having a fifth closed layer of 16 alpha particles

[en] Four major families of copper-oxide based high T/sub c/ superconductors have been identified by a number of research groups. It is now well established that the superconductivity is associated with the layers of copper-oxide and that some of the remaining structural building blocks in each primitive cell act as electron acceptors which induce the holes in the copper-oxide layers necessary for superconductivity. 9 refs., 4 figs

[en] This analysis of the bonding in the excited molecular states of ¹²C, ¹⁶O, ²⁰Ne, ²⁴Mg, ²⁸Si and ³²S as proposed by Ikeda is based on the concept of meson bonds. This shows a very regular variation in the bonding between alpha particles in each nucleus as the excitation energy changes. Furthermore, the most excited state of each nucleus is shown to be less strongly bound than are the less excited states. (brief report)

[en] As an emerging effective approach to nonlinear robust control, simplex sliding mode control demonstrates some attractive features not possessed by the conventional sliding mode control method, from both theoretical and practical points of view. However, no systematic approach is currently available for computing the simplex control vectors in nonlinear sliding mode control. In this paper, chaos-based optimization is exploited so as to develop a systematic approach to seeking the simplex control vectors; particularly, the flexibility of simplex control is enhanced by making the simplex control vectors dependent on the Euclidean norm of the sliding vector rather than being constant, which result in both reduction of the chattering and speedup of the convergence. Computer simulation on a nonlinear uncertain system is given to illustrate the effectiveness of the proposed control method