17,848 research outputs found

    The analysis of temporal variations in regional models of the Sargasso Sea from GEOS-3 altimetry

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    The dense coverage of short pulse mode GEOS-3 altimeter data in the western North Atlantic provides a basis for studying time variations in the sea surface heights in the Sargasso Sea. Two techniques are utilized: the method of regional models, and the analysis of overlapping passes. An 88 percent correlation is obtained between the location of cyclonic eddies obtained from infrared imagery and sea surface height minima in the altimeter models. This figure drops to 59 percent in the case of correlations with maxima and minima of surface temperature fields. The analysis of overlapping passes provides a better picture of instantaneous sea state through wavelengths greater than 30 km. The variability of the Sargasso Sea through wavelengths between 150 km and 5000 km is estimated at + or - 28 cm. This value is in reasonable agreement with oceanographic estimates and is compatible with the eddy kinetic energy of a wind driven circulation

    Electromotive forces and the Meissner effect puzzle

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    In a voltaic cell, positive (negative) ions flow from the low (high) potential electrode to the high (low) potential electrode, driven by an `electromotive force' which points in opposite direction and overcomes the electric force. Similarly in a superconductor charge flows in direction opposite to that dictated by the Faraday electric field as the magnetic field is expelled in the Meissner effect. The puzzle is the same in both cases: what drives electric charges against electromagnetic forces? I propose that the answer is also the same in both cases: kinetic energy lowering, or `quantum pressure'

    Superconductivity from Undressing. II. Single Particle Green's Function and Photoemission in Cuprates

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    Experimental evidence indicates that the superconducting transition in high TcT_c cuprates is an 'undressing' transition. Microscopic mechanisms giving rise to this physics were discussed in the first paper of this series. Here we discuss the calculation of the single particle Green's function and spectral function for Hamiltonians describing undressing transitions in the normal and superconducting states. A single parameter, Υ\Upsilon, describes the strength of the undressing process and drives the transition to superconductivity. In the normal state, the spectral function evolves from predominantly incoherent to partly coherent as the hole concentration increases. In the superconducting state, the 'normal' Green's function acquires a contribution from the anomalous Green's function when Υ \Upsilon is non-zero; the resulting contribution to the spectral function is positivepositive for hole extraction and negativenegative for hole injection. It is proposed that these results explain the observation of sharp quasiparticle states in the superconducting state of cuprates along the (π,0)(\pi,0) direction and their absence along the (π,π)(\pi,\pi) direction.Comment: figures have been condensed in fewer pages for easier readin

    Spherical agglomeration of superconducting and normal microparticles with and without applied electric field

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    It was reported by R. Tao and coworkers that in the presence of a strong electric field superconducting microparticles assemble into balls of macroscopic dimensions. Such a finding has potentially important implications for the understanding of the fundamental physics of superconductors. However, we report here the results of experimental studies showing that (i) ball formation also occurs in the absence of an applied electric field, (ii) the phenomenon also occurs at temperatures above the superconducting transition temperature, and (iii) it can also occur for non-superconducting materials. Possible origins of the phenomenon are discussed.Comment: Small changes in response to referee's comments. To be published in Phys. Rev.

    Functional Flow Diagrams: A New Tool For Engineering Management

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    Technical management, often done by seat of the pants during the airplane age, is becoming more systematized and sophisticated to meet the challenge of the space age. Man\u27s presence in space means that there are now many more alternatives to accomplishing a function. Functional flow diagrams present the technical manager with a rapid, comprehensive way to evaluate all the alternatives and the consequences of his decisions on the rest of the system. They also provide him with a tool to check the system design to assure that all the requirements are satisfied. The latest techniques are typified in the Air Force System Command Manuals 375-1* 2, 3, ^, and 5. One of these, AFSCM 375-5, System Engineering Management Procedures , describes specific system engineering methods to be followed by recipients of large Air Force contracts. This paper describes the preparation of functional flow diagrams which will be of value to both engineers and their technical managers. The illustrations are typical for a Manned Orbiting Laboratory (MOL) Program. Functional flow diagrams were prepared on earlier programs, including Titan II and Titan III, and are one of the required products of AFSCM 375-5- Traditionally, these old flow diagrams take the form of sequences of functions needed to accomplish a desired operation or mission (see Figure l), Such diagrams, even when carried out to a lower indenture (see Figure 2), are of limited value. They tend to lag the conceptual and design efforts. The new type of functional flow diagram (see Figure 3) starts where the traditional type ended. Let us see how Figure 3 vas developed, what it tells us, and how it can be used

    Towards an understanding of hole superconductivity

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    From the very beginning K. Alex M\"uller emphasized that the materials he and George Bednorz discovered in 1986 were holehole superconductors. Here I would like to share with him and others what I believe to be thethe key reason for why high TcT_c cuprates as well as all other superconductors are hole superconductors, which I only came to understand a few months ago. This paper is dedicated to Alex M\"uller on the occasion of his 90th birthday.Comment: Dedicated to Alex M\"uller on the Occasion of his 90th Birthday. arXiv admin note: text overlap with arXiv:1703.0977

    Superconductivity from Undressing

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    Photoemission experiments in high TcT_c cuprates indicate that quasiparticles are heavily 'dressed' in the normal state, particularly in the low doping regime. Furthermore these experiments show that a gradual undressing occurs both in the normal state as the system is doped and the carrier concentration increases, as well as at fixed carrier concentration as the temperature is lowered and the system becomes superconducting. A similar picture can be inferred from optical experiments. It is argued that these experiments can be simply understood with the single assumption that the quasiparticle dressing is a function of the local carrier concentration. Microscopic Hamiltonians describing this physics are discussed. The undressing process manifests itself in both the one-particle and two-particle Green's functions, hence leads to observable consequences in photoemission and optical experiments respectively. An essential consequence of this phenomenology is that the microscopic Hamiltonians describing it break electron-hole symmetry: these Hamiltonians predict that superconductivity will only occur for carriers with hole-like character, as proposed in the theory of hole superconductivity

    Relational lattices via duality

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    The natural join and the inner union combine in different ways tables of a relational database. Tropashko [18] observed that these two operations are the meet and join in a class of lattices-called the relational lattices- and proposed lattice theory as an alternative algebraic approach to databases. Aiming at query optimization, Litak et al. [12] initiated the study of the equational theory of these lattices. We carry on with this project, making use of the duality theory developed in [16]. The contributions of this paper are as follows. Let A be a set of column's names and D be a set of cell values; we characterize the dual space of the relational lattice R(D, A) by means of a generalized ultrametric space, whose elements are the functions from A to D, with the P (A)-valued distance being the Hamming one but lifted to subsets of A. We use the dual space to present an equational axiomatization of these lattices that reflects the combinatorial properties of these generalized ultrametric spaces: symmetry and pairwise completeness. Finally, we argue that these equations correspond to combinatorial properties of the dual spaces of lattices, in a technical sense analogous of correspondence theory in modal logic. In particular, this leads to an exact characterization of the finite lattices satisfying these equations.Comment: Coalgebraic Methods in Computer Science 2016, Apr 2016, Eindhoven, Netherland

    Low Energy Properties of the Random Spin-1/2 Ferromagnetic-Antiferromagnetic Heisenberg Chain

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    The low energy properties of the spin-1/2 random Heisenberg chain with ferromagnetic and antiferromagnetic interactions are studied by means of the density matrix renormalization group (DMRG) and real space renormalization group (RSRG) method for finite chains. The results of the two methods are consistent with each other. The deviation of the gap distribution from that of the random singlet phase and the formation of the large-spin state is observed even for relatively small systems. For a small fraction of the ferromagnetic bond, the effect of the crossover to the random singlet phase on the low temperature susceptibility and specific heat is discussed. The crossover concentration of the ferromagnetic bond is estimated from the numerical data.Comment: 11 pages, revtex, figures upon reques

    R-parity Conserving Supersymmetry, Neutrino Mass and Neutrinoless Double Beta Decay

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    We consider contributions of R-parity conserving softly broken supersymmetry (SUSY) to neutrinoless double beta (\znbb) decay via the (B-L)-violating sneutrino mass term. The latter is a generic ingredient of any weak-scale SUSY model with a Majorana neutrino mass. The new R-parity conserving SUSY contributions to \znbb are realized at the level of box diagrams. We derive the effective Lagrangian describing the SUSY-box mechanism of \znbb-decay and the corresponding nuclear matrix elements. The 1-loop sneutrino contribution to the Majorana neutrino mass is also derived. Given the data on the \znbb-decay half-life of 76^{76}Ge and the neutrino mass we obtain constraints on the (B-L)-violating sneutrino mass. These constraints leave room for accelerator searches for certain manifestations of the 2nd and 3rd generation (B-L)-violating sneutrino mass term, but are most probably too tight for first generation (B-L)-violating sneutrino masses to be searched for directly.Comment: LATEX, 29 pages + 4 (uuencoded) figures appende
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