25,810 research outputs found

    Towards a quantum field theory of primitive string fields

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    We denote generating functions of massless even higher spin fields "primitive string fields" (PSF's). In an introduction we present the necessary definitions and derive propagators and currents of these PDF's on flat space. Their off-shell cubic interaction can be derived after all off-shell cubic interactions of triplets of higher spin fields have become known [2],[3]. Then we discuss four-point functions of any quartet of PSF's. In subsequent sections we exploit the fact that higher spin field theories in AdSd+1AdS_{d+1} are determined by AdS/CFT correspondence from universality classes of critical systems in dd dimensional flat spaces. The O(N) invariant sectors of the O(N) vector models for 1N1\leq N \leq \infty play for us the role of "standard models", for varying NN, they contain e.g. the Ising model for N=1 and the spherical model for N=N=\infty. A formula for the masses squared that break gauge symmetry for these O(N) classes is presented for d = 3. For the PSF on AdSAdS space it is shown that it can be derived by lifting the PSF on flat space by a simple kernel which contains the sum over all spins. Finally we use an algorithm to derive all symmetric tensor higher spin fields. They arise from monomials of scalar fields by derivation and selection of conformal (quasiprimary) fields. Typically one monomial produces a multiplet of spin ss conformal higher spin fields for all s4s \geq 4, they are distinguished by their anomalous dimensions (in CFT3CFT_3) or by their mass (in AdS4AdS_4). We sum over these multiplets and the spins to obtain "string type fields", one for each such monomial.Comment: 16 pages,Late

    The Rocketdyne Multifunction Tester. Part 2: Operation of a Radial Magnetic Bearing as an Excitation Source

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    The operation of the magnetic bearing used as an excitation source in the Rocketdyne Multifunction Tester is described. The tester is scheduled for operation during the summer of 1990. The magnetic bearing can be used in two control modes: (1) open loop mode, in which the magnetic bearing operates as a force actuator; and (2) closed loop mode, in which the magnetic bearing provides shaft support. Either control mode can be used to excite the shaft; however, response of the shaft in the two control modes is different due to the alteration of the eigenvalues by closed loop mode operation. A rotordynamic model is developed to predict the frequency response of the tester due to excitation in either control mode. Closed loop mode excitation is shown to be similar to the excitation produced by a rotating eccentricity in a conventional bearing. Predicted frequency response of the tester in the two control modes is compared, and the maximum response is shown to be the same for the two control modes when synchronous unbalance loading is not considered. The analysis shows that the response of this tester is adequate for the extraction of rotordynamic stiffness, damping, and inertia coefficients over a wide range of test article stiffnesses

    Wheel–rail contact: experimental study of the creep forces–creepage relationships

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    The wheel–rail contact problem plays an important role in the simulation methods used to solve railway dynamics problems. As a consequence, many different mathematical models have been developed to calculate wheel–rail contact forces. However, most of them tackle this problem purely from a theoretical point of view and need to be experimentally validated. Such validation could also reveal the influence of certain parameters not taken into account in the mathematical developments. This paper presents the steps followed in building a scaled test-bench to experimentally characterise the wheel–rail contact problem. The results of the longitudinal contact force as a function of the longitudinal creepage are obtained and the divergences with respect to Kalker's simplified theory are analysed. The influence of lateral creepage, angular velocity and certain contaminants such as cutting fluid or high positive friction modifier is also discussed

    The Measure of the Orthogonal Polynomials Related to Fibonacci Chains: The Periodic Case

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    The spectral measure for the two families of orthogonal polynomial systems related to periodic chains with N-particle elementary unit and nearest neighbour harmonic interaction is computed using two different methods. The interest is in the orthogonal polynomials related to Fibonacci chains in the periodic approximation. The relation of the measure to appropriately defined Green's functions is established.Comment: 19 pages, TeX, 3 scanned figures, uuencoded file, original figures on request, some misprints corrected, tbp: J. Phys.

    Polaronic slowing of fermionic impurities in lattice Bose-Fermi mixtures

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    We generalize the application of small polaron theory to ultracold gases of Ref. [\onlinecite{jaksch_njp1}] to the case of Bose-Fermi mixtures, where both components are loaded into an optical lattice. In a suitable range of parameters, the mixture can be described within a Bogoliubov approach in the presence of fermionic (dynamic) impurities and an effective description in terms of polarons applies. In the dilute limit of the slow impurity regime, the hopping of fermionic particles is exponentially renormalized due to polaron formation, regardless of the sign of the Bose-Fermi interaction. This should lead to clear experimental signatures of polaronic effects, once the regime of interest is reached. The validity of our approach is analyzed in the light of currently available experiments. We provide results for the hopping renormalization factor for different values of temperature, density and Bose-Fermi interaction for three-dimensional 87Rb40K^{87}\rm{Rb}-^{40}\rm{K} mixtures in optical lattice.Comment: 13 pages, 5 figure

    Potential competitive effects on U.S. bank credit card lending from the proposed bifurcated application of Basel II

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    This paper analyzes the potential competitive effects of the proposed bifurcated application of Basel II capital regulations in the United States on bank credit card lending activities. For this purpose, the authors consider the Basel II regulations as stated in the June 2004 Basel Committee Framework Agreement. ; Also issued as Payment Cards Center Discussion Paper No. 05-21 ; Superseded by Working Paper 07-09Basel capital accord ; Credit cards
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