20,329 research outputs found

    The effect of circumferential distortion on fan performance at two levels of blade loading

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    Single stage fans designed for two levels of pressure ratio or blade loading were subjected to screen-induced circumferential distortions of 90-degree extent. Both fan rotors were designed for a blade tip speed of 425 m/sec, blade solidity of 1.3 and a hub-to-tip radius ratio of 0.5. Circumferential measurements of total pressure, temperature, static pressure, and flow angle were obtained at the hub, mean and tip radii at five axial stations. Rotor loading level did not appear to have a significant influence on rotor response to distorted flow. Losses in overall pressure ratio due to distortion were most severe in the stator hub region of the more highly loaded stage. At the near stall operating condition tip and hub regions of (either) rotor demonstrated different response characteristics to the distorted flow. No effect of loading was apparent on interactions between rotor and upstream distorted flow fields

    Interpolation and harmonic majorants in big Hardy-Orlicz spaces

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    Free interpolation in Hardy spaces is caracterized by the well-known Carleson condition. The result extends to Hardy-Orlicz spaces contained in the scale of classical Hardy spaces HpH^p, p>0p>0. For the Smirnov and the Nevanlinna classes, interpolating sequences have been characterized in a recent paper in terms of the existence of harmonic majorants (quasi-bounded in the case of the Smirnov class). Since the Smirnov class can be regarded as the union over all Hardy-Orlicz spaces associated with a so-called strongly convex function, it is natural to ask how the condition changes from the Carleson condition in classical Hardy spaces to harmonic majorants in the Smirnov class. The aim of this paper is to narrow down this gap from the Smirnov class to ``big'' Hardy-Orlicz spaces. More precisely, we characterize interpolating sequences for a class of Hardy-Orlicz spaces that carry an algebraic structure and that are strictly bigger than p>0Hp\bigcup_{p>0} H^p. It turns out that the interpolating sequences are again characterized by the existence of quasi-bounded majorants, but now the weights of the majorants have to be in suitable Orlicz spaces. The existence of harmonic majorants in such Orlicz spaces will also be discussed in the general situation. We finish the paper with an example of a separated Blaschke sequence that is interpolating for certain Hardy-Orlicz spaces without being interpolating for slightly smaller ones.Comment: 19 pages, 2 figure

    Electromagnetic Interaction in the System of Multimonopoles and Vortex Rings

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    Behavior of static axially symmetric monopole-antimonopole and vortex ring solutions of the SU(2) Yang-Mills-Higgs theory in an external uniform magnetic field is considered. It is argued that the axially symmetric monopole-antimonopole chains and vortex rings can be treated as a bounded electromagnetic system of the magnetic charges and the electric current rings. The magnitude of the external field is a parameter which may be used to test the structure of the static potential of the effective electromagnetic interaction between the monopoles with opposite orientation in the group space. It is shown that for a non-BPS solutions there is a local minimum of this potential.Comment: 10 pages, 12 figures, some minor corrections, version to appear in Phys. Rev.

    On Which Length Scales Can Temperature Exist in Quantum Systems?

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    We consider a regular chain of elementary quantum systems with nearest neighbor interactions and assume that the total system is in a canonical state with temperature TT. We analyze under what condition the state factors into a product of canonical density matrices with respect to groups of nn subsystems each, and when these groups have the same temperature TT. While in classical mechanics the validity of this procedure only depends on the size of the groups nn, in quantum mechanics the minimum group size nminn_{\text{min}} also depends on the temperature TT ! As examples, we apply our analysis to different types of Heisenberg spin chains.Comment: To appear in: Proceedings of the SPQS conference, J. Phys. Soc. Jpn. 74 (2005) Supp

    Environment-Mediated Quantum State Transfer

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    We propose a scheme for quantum state transfer(QST) between two qubits which is based on their individual interaction with a common boson environment. The corresponding single mode spin-boson Hamiltonian is solved by mapping it onto a wave propagation problem in a semi-infinite ladder and the fidelity is obtained. High fidelity occurs when the qubits are equally coupled to the boson while the fidelity becomes smaller for nonsymmetric couplings. The complete phase diagram for such an arbitrary QST mediated by bosons is discussed.Comment: 6 pages and 5 figure

    Ground-State and Domain-Wall Energies in the Spin-Glass Region of the 2D ±J\pm J Random-Bond Ising Model

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    The statistics of the ground-state and domain-wall energies for the two-dimensional random-bond Ising model on square lattices with independent, identically distributed bonds of probability pp of Jij=1J_{ij}= -1 and (1p)(1-p) of Jij=+1J_{ij}= +1 are studied. We are able to consider large samples of up to 3202320^2 spins by using sophisticated matching algorithms. We study L×LL \times L systems, but we also consider L×ML \times M samples, for different aspect ratios R=L/MR = L / M. We find that the scaling behavior of the ground-state energy and its sample-to-sample fluctuations inside the spin-glass region (pcp1pcp_c \le p \le 1 - p_c) are characterized by simple scaling functions. In particular, the fluctuations exhibit a cusp-like singularity at pcp_c. Inside the spin-glass region the average domain-wall energy converges to a finite nonzero value as the sample size becomes infinite, holding RR fixed. Here, large finite-size effects are visible, which can be explained for all pp by a single exponent ω2/3\omega\approx 2/3, provided higher-order corrections to scaling are included. Finally, we confirm the validity of aspect-ratio scaling for R0R \to 0: the distribution of the domain-wall energies converges to a Gaussian for R0R \to 0, although the domain walls of neighboring subsystems of size L×LL \times L are not independent.Comment: 11 pages with 15 figures, extensively revise

    Statistics of lowest excitations in two dimensional Gaussian spin glasses

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    A detailed investigation of lowest excitations in two-dimensional Gaussian spin glasses is presented. We show the existence of a new zero-temperature exponent lambda describing the relative number of finite-volume excitations with respect to large-scale ones. This exponent yields the standard thermal exponent of droplet theory theta through the relation, theta=d(lambda-1). Our work provides a new way to measure the thermal exponent theta without any assumption about the procedure to generate typical low-lying excitations. We find clear evidence that theta < theta_{DW} where theta_{DW} is the thermal exponent obtained in domain-wall theory showing that MacMillan excitations are not typical.Comment: 4 pages, 3 figures, (v2) revised version, (v3) corrected typo

    On the merit of a Central Limit Theorem-based approximation in statistical physics

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    The applicability conditions of a recently reported Central Limit Theorem-based approximation method in statistical physics are investigated and rigorously determined. The failure of this method at low and intermediate temperature is proved as well as its inadequacy to disclose quantum criticalities at fixed temperatures. Its high temperature predictions are in addition shown to coincide with those stemming from straightforward appropriate expansions up to (k_B T)^(-2). Our results are clearly illustrated by comparing the exact and approximate temperature dependence of the free energy of some exemplary physical systems.Comment: 12 pages, 1 figur
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