6,095 research outputs found

    Antimatter propulsion, status and prospects

    Get PDF
    The use of advanced propulsion techniques must be considered if the currently envisioned launch date of the manned Mars mission were delayed until 2020 or later. Within the next thirty years, technological advances may allow such methods as beaming power to the ship, inertial-confinement fusion, or mass-conversion of antiprotons to become feasible. A propulsion system with an ISP of around 5000 s would allow the currently envisioned mission module to fly to Mars in 3 months and would require about one million pounds to be assembled in Earth orbit. Of the possible methods to achieve this, the antiproton mass-conversion reaction offers the highest potential, the greatest problems, and the most fascination. Increasing the production rates of antiprotons is a high priority task at facilities around the world. The application of antiprotons to propulsion requires the coupling of the energy released in the mass-conversion reaction to thrust-producing mechanisms. Recent proposals entail using the antiprotons to produce inertial confinement fusion or to produce negative muons which can catalyze fusion. By increasing the energy released per antiproton, the effective cost, (dollars/joule) can be reduced. These proposals and other areas of research can be investigated now. These short term results will be important in assessing the long range feasibility of an antiproton powered engine

    Educational Problems in Writing Chemical Formulae and Equations

    Get PDF
    The difficulties existing for many pupils in the areas of formulae and equations and the belief that many of these problems were due to maturity barriers, led to the inauguration of this study in 1970. A preliminary survey was made of the situation extant in 1970 concerning these topics. This revealed a very confused picture with wide variation of teacher approach. The most obvious problem was one of over-complexity in formulae and equations. Teachers were teaching with little or no regard for the developmental ideas of Piaget et al. This problem was investigated at school level by a test based on a Gagne net for the writing of formulae and by a questionnaire. This test was examined in depth and confirmed the indications gathered in the preliminary survey. Pupils did not appear to reason logically when writing formulae but rather committed certain common formulae to memory, and failure at one step in the thought process did not appear to affect performance in the next. The very high number of pupils unable to handle proportion (71%) calculations from equations (97%) was disturbing, (the problem may be purely mathematical,) and many pupils showed a lack of understanding of even the most basic principles e.g. nomenclature, formation,of ions. Pupils seemed able to cope with individual steps in e. g. formula writing, but could not handle all the material "en bloc" when it was presented in a very short time (2-3 months). This meant that overall performance was very poor (28% correct). A re-run of part of this test confirmed these results. The questionnaire revealed that pupils tended to underestimate the difficulty of many topics and that teachers were more consistent than them in their estimates of difficulty. The teaching order of the 'O' grade course in Chemistry was then examined in the light of the degree of complexity in formulae and equations needed for each section. A revised teaching order, which was basically 'organic first' was drawn up using the principle of gradual revelation of these topics. To evaluate this revised order a maturity study was set up, having both experimental and control groups. The progress of the groups was monitored by a series of short tests, the results of which, and the 1973 'O' grade examination in Chemistry were analysed. No significant differences were found, but following the revised order did not disadvantage pupils over those following the standard orders. In fact there was some evidence to show that the revised order had achieved for these pupils, a higher level of understanding on the more difficult topics, especially calculations from equations and the mole. They also were more consistent in their level of performance on writing formulae. A detailed analysis of the last test (an overall revision of the work) was carried out and showed the same problems as were evident in the Gagne study e. g. interpretation of nomenclature such as the difference between - IDE and - ITE compounds. Some topics appeared to be still beyond the majority of pupils e. g. (i) extrapolation from Na2CO3 to Na2SiO3 (12%) (ii) writing balanced equations (20%) (iii) calculations from equations (20%). However pupils did seem to grasp the mathematical rules for formulae writing reasonably competently. A similar questionnaire to that used in the first investigation revealed that in general the revised group found the course easier than the control groups and that pupils now overestimated the difficulty of those topics previously underestimated. A final survey in 1974 showed a situation on the one hand eased by the removal of a recall barrier in formula writing and on the other worsened by the choice of the correct level of complexity of formulae to be used in any questions being left to the pupil. Recommendations were made for lessening the amount of conceptually difficult material (Piaget Stage 3) in the 'O' grade syllabus and its replacement by work involving lower order skills, including purely practical ones

    The Schwinger SU(3) construction - I: Multiplicity problem and relation to induced representations

    Full text link
    The Schwinger oscillator operator representation of SU(3) is analysed with particular reference to the problem of multiplicity of irreducible representations. It is shown that with the use of an Sp(2,R)Sp(2,R) unitary representation commuting with the SU(3) representation, the infinity of occurrences of each SU(3) irreducible representation can be handled in complete detail. A natural `generating representation' for SU(3), containing each irreducible representation exactly once, is identified within a subspace of the Schwinger construction; and this is shown to be equivalent to an induced representation of SU(3).Comment: Latex, 25 page

    BRST quantization of matrix models with constraints and two-dimensional Yang-Mills theory on the cylinder

    Get PDF
    BRST quantization of the one-dimensional constrained matrix model which describes two-dimensional Yang-Mills theory on the cylinder is performed. Classical and quantum BRST generators and BRST-invariant hamiltonians are constructed. Evolution operator is expressed in terms of BRST path integral. Advantages of the BRST quantization over the reduced phase space approach leading to the theory of NN free fermions are discussed.Comment: 8 page

    Study protocol for a randomised controlled trial of electronic cigarettes versus nicotine patch for smoking cessation

    Get PDF
    PMCID: PMC3602285This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited

    Noncommutative symmetric functions and Laplace operators for classical Lie algebras

    Get PDF
    New systems of Laplace (Casimir) operators for the orthogonal and symplectic Lie algebras are constructed. The operators are expressed in terms of paths in graphs related to matrices formed by the generators of these Lie algebras with the use of some properties of the noncommutative symmetric functions associated with a matrix. The decomposition of the Sklyanin determinant into a product of quasi-determinants play the main role in the construction. Analogous decomposition for the quantum determinant provides an alternative proof of the known construction for the Lie algebra gl(N).Comment: 25 page

    Einstein-Weyl structures and Bianchi metrics

    Get PDF
    We analyse in a systematic way the (non-)compact four dimensional Einstein-Weyl spaces equipped with a Bianchi metric. We show that Einstein-Weyl structures with a Class A Bianchi metric have a conformal scalar curvature of constant sign on the manifold. Moreover, we prove that most of them are conformally Einstein or conformally K\"ahler ; in the non-exact Einstein-Weyl case with a Bianchi metric of the type VII0,VIIIVII_0, VIII or IXIX, we show that the distance may be taken in a diagonal form and we obtain its explicit 4-parameters expression. This extends our previous analysis, limited to the diagonal, K\"ahler Bianchi IXIX case.Comment: Latex file, 12 pages, a minor modification, accepted for publication in Class. Quant. Gra

    PHP111 PREDICTING PREVENTIVE CARE SERVICE UTILIZATION IN A UNITED STATES POPULATION

    Get PDF

    Radiation reaction and renormalization in classical electrodynamics of point particle in any dimension

    Get PDF
    The effective equations of motion for a point charged particle taking account of radiation reaction are considered in various space-time dimensions. The divergencies steaming from the pointness of the particle are studied and the effective renormalization procedure is proposed encompassing uniformly the cases of all even dimensions. It is shown that in any dimension the classical electrodynamics is a renormalizable theory if not multiplicatively beyond d=4. For the cases of three and six dimensions the covariant analogs of the Lorentz-Dirac equation are explicitly derived.Comment: minor changes in concluding section, misprints corrected, LaTeX2e, 15 page
    corecore