9,970 research outputs found

    Magnification Control in Self-Organizing Maps and Neural Gas

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    We consider different ways to control the magnification in self-organizing maps (SOM) and neural gas (NG). Starting from early approaches of magnification control in vector quantization, we then concentrate on different approaches for SOM and NG. We show that three structurally similar approaches can be applied to both algorithms: localized learning, concave-convex learning, and winner relaxing learning. Thereby, the approach of concave-convex learning in SOM is extended to a more general description, whereas the concave-convex learning for NG is new. In general, the control mechanisms generate only slightly different behavior comparing both neural algorithms. However, we emphasize that the NG results are valid for any data dimension, whereas in the SOM case the results hold only for the one-dimensional case.Comment: 24 pages, 4 figure

    Killing spinors in supergravity with 4-fluxes

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    We study the spinorial Killing equation of supergravity involving a torsion 3-form \T as well as a flux 4-form \F. In dimension seven, we construct explicit families of compact solutions out of 3-Sasakian geometries, nearly parallel \G_2-geometries and on the homogeneous Aloff-Wallach space. The constraint \F \cdot \Psi = 0 defines a non empty subfamily of solutions. We investigate the constraint \T \cdot \Psi = 0, too, and show that it singles out a very special choice of numerical parameters in the Killing equation, which can also be justified geometrically

    ENERAPAN POS (PROSEDUR OPERASIONAL STANDAR) PADA PROSES PEMBELAJARAN PRAKTIK DI BENGKEL PEMESINAN SEBAGAI UPAYA MENINGKATKAN KUALITAS PEMBELAJARAN PRAKTIK

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    ABSTRAK Matakuliah Proses Pemesinan merupakan matakuliah praktik yang mengajarkan keterampilan / kompetensi di bidang pemesinan. Kompetensi pemesinan sebagai kompetensi produktif merupakan cirikhas yang membedakan antara Jurusan Pendidikan Teknik Mesin dengan jurusan lain. Usaha peningkatan kualitas pembelajaran, khususnya untuk pembelajaran praktik pemesinan, salah satu diantaranya adalah dengan menerapkan Prosedur Operasional Standar (POS). Penerapan POS dalam pembelajaran praktik pemesinan ini diharapkan dapat meningkatkan efektifitas pembelajaran yang berlangsung, dimana penerapan POS ini menuntut semua pihak yang terlibat dalam proses pembelajaran (dosen, mahasiswa, teknisi) untuk melakukan pekerjaannya dengan prosedur standar yang telah ditentukan. Penelitian ini ditujukan untuk melakukan evaluasi terhadap materi POS yang sudah ada yang dilakukan dengan langkah-langkah yaitu verifikasi silabi dengan kompetensi, verifikasi job praktik dengan silabi, dan menyempurnakan POS yang sudah ada. Dengan penerapan POS ini dapat dilihat indikator keberhasilannya yaitu waktu yang dibutuhkan untuk menyelesaikan tiap-tiap job praktik lebih cepat. Penelitian yang telah dilaksanakan menghasilkan data yaitu kesesuaian silabi dengan kompetensi mata kuliah Proses Pemesinan 5 sebesar 75%, mata kuliah Proses Pemesinan 3 sebesar 66,6%, mata kuliah Proses Pemesinan 1 sebesar 100%. Kesesuaian job praktik dengan silabi mata kuliah Proses Pemesinan 5 sebesar 80%, mata kuliah Proses Pemesinan 3 sebesar 90%, mata kuliah Proses Pemesinan 1 sebesar 100%. POS yang telah disempurnakan dapat menghemat waktu penyelesaian tiap-tiap job praktik hingga 30%. Kata kunci: Proses Pemesinan, Prosedur Operasional Standa

    The Functional Derivation of Master Equations

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    Master equations describe the quantum dynamics of open systems interacting with an environment. They play an increasingly important role in understanding the emergence of semiclassical behavior and the generation of entropy, both being related to quantum decoherence. Presently we derive the exact master equation for a homogeneous scalar Higgs or inflaton like field coupled to an environment field represented by an infinite set of harmonic oscillators. Our aim is to demonstrate a derivation directly from the path integral representation of the density matrix propagator. Applications and generalizations of this result are discussed.Comment: 10 pages; LaTex. - Contribution to the workshop Hadron Physics VI, March 1998, Florianopolis (Brazil); proceedings, E. Ferreira et al., eds. (World Scientific). Replaced by slightly modified published versio

    Ledoux-Convection in Protoneutron Stars --- a Clue to Supernova Nucleosynthesis?

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    Two-dimensional hydrodynamical simulations of the deleptonization of a newly formed neutron star were performed. Driven by negative lepton fraction and entropy gradients, convection starts near the neutrinosphere about 20-30 ms after core bounce, but moves deeper into the protoneutron star, and after about one second the whole protoneutron star is convective. The deleptonization of the star proceeds much faster than in the corresponding spherically symmetrical model because the lepton flux and the neutrino luminosities increase by up to a factor of two. The convection below the neutrinosphere raises the neutrinospheric temperatures and mean energies of the emitted neutrinos by 10-20%. This can have important implications for the supernova explosion mechanism and changes the detectable neutrino signal from the Kelvin-Helmholtz cooling of the protoneutron star. In particular, the enhanced electron neutrino flux relative to the electron antineutrino flux during the early post-bounce evolution might solve the overproduction problem of certain elements in the neutrino-heated ejecta in models of type-II supernova explosions.Comment: 17 pages, LaTeX, 8 postscript figures, uses epsf.sty. To appear in ApJ 473 (Letters), 1996 December 1

    Author Identification in Economics, ... and Beyond

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    Identifying authorship correctly and efficiently is a difficult problem when the literature is abundant, but poorly recorded. Homonyms are tedious to differentiate. This paper describes how the field of economics has organized itself with respect to author identification. We describe the RePEc project with a special emphasis on the RePEc Author Service. We then discuss how the concept is currently being expanded to the entire scientific body with the AuthorClaim project

    FFT for the APE Parallel Computer

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    We present a parallel FFT algorithm for SIMD systems following the `Transpose Algorithm' approach. The method is based on the assignment of the data field onto a 1-dimensional ring of systolic cells. The systolic array can be universally mapped onto any parallel system. In particular for systems with next-neighbour connectivity our method has the potential to improve the efficiency of matrix transposition by use of hyper-systolic communication. We have realized a scalable parallel FFT on the APE100/Quadrics massively parallel computer, where our implementation is part of a 2-dimensional hydrodynamics code for turbulence studies. A possible generalization to 4-dimensional FFT is presented, having in mind QCD applications.Comment: 17 pages, 13 figures, figures include

    Coupled Ito equations of continuous quantum state measurement, and estimation

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    We discuss a non-linear stochastic master equation that governs the time-evolution of the estimated quantum state. Its differential evolution corresponds to the infinitesimal updates that depend on the time-continuous measurement of the true quantum state. The new stochastic master equation couples to the two standard stochastic differential equations of time-continuous quantum measurement. For the first time, we can prove that the calculated estimate almost always converges to the true state, also at low-efficiency measurements. We show that our single-state theory can be adapted to weak continuous ensemble measurements as well.Comment: 5 pages, RevTeX4. In version v2 some minor revisions and clarifications have been incorporated. Moreover, a new reference has been included. Accepted for publication in Journal of Physics A: Mathematical and Genera
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