320 research outputs found

    Design of Experiments under Constraints

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    This paper was done in collaboration between the System and Decision Sciences Area (SDS) and the Adaptive Resource Policy Project (ARP). It faces the problem of optimal experimental design. This problem arises in adaptive policy making at the stage of estimating a model's parameters. It can be considered as an optimization problem with both objective functions and constraints dependent upon probabilistic measures. Methods for dealing with such problems have recently been developed in SDS. In this paper, these methods are applied to optimal experimental design which allows us to get nontrivial results both in statistics and optimization theory

    Momentum Distributions of Particles from Three--Body Halo Fragmentation: Final State Interactions

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    Momentum distributions of particles from nuclear break-up of fast three-body halos are calculated consistently, and applied to 11^{11}Li. The same two-body interactions between the three particles are used to calculate the ground state structure and the final state of the reaction processes. We reproduce the available momentum distributions from 11^{11}Li fragmentation, together with the size and energy of 11^{11}Li, with a neutron-core relative state containing a pp-state admixture of 20\%-30\%. The available fragmentation data strongly suggest an ss-state in 10^{10}Li at about 50 keV, and indicate a pp-state around 500 keV.Comment: 11 pages (RevTeX), 3 Postscript figures (uuencoded postscript file attached at the end of the LaTeX file). To be published in Phys. Rev.

    Possible role of some groups in the structure and function of HIV-1 protease as revealed by molecular modeling studies

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    AbstractRetroviral proteases belong to the class of aspartic proteases. A molecular model of HIV-1 protease has been built on the basis of the consensus template specific for the domains of these enzymes. The template region comprises more than a half of the HIV-1 protease monomer structure, it includes the active site, formed at the junction of the two monomers, binding pockets of the enzyme, and some other molecular segments. These regions can be more conveniently described than other parts of the structure. Some properties of the HIV-1 protease molecule are discussed, as well as of probable inhibitors. The properties of the model structure are in good agreement with the recent results of crystallographic studies of Rous sarcoma virus protease

    The X1 catalogue of positions and proper motions of faint stars around the ICRF sources

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    We present a new catalogue of faint astrometric reference stars around ICRF sources of northern hemisphere. The X1 catalogue is obtained at the Institute of Astronomy of the V.N. Karazin Kharkiv National University and contains about 1.3 million positions and proper motions of stars from 10m to 19m within 330 1° ×1° fields. Mean positions and proper motions of stars were derived from reprocessing and astrometric reduction of digitized images of Schmidt plates POSS-I and POSS-II sky surveys obtained from USNOFS PMM Image Archive. The Tycho-2 stars were used as reference stars. The mean errors of the positions at mean epoch are 50 to 100 mas, depending on magnitude and particular field. Proper motions errors are about 2.5 to 5 mas/yr depending on magnitude. Estimated external errors are close to internal errors mentioned. The source data, brief outlines of the image processing and reduction techniques, main features of the catalogue, as well as some results of external comparisons are presented

    Three-body decays: structure, decay mechanism and fragment properties

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    We discuss the three-body decay mechanisms of many-body resonances. R-matrix sequential description is compared with full Faddeev computation. The role of the angular momentum and boson symmetries is also studied. As an illustration we show the computed α\alpha-particle energy distribution after the decay of 12C(1^+) resonance at 12.7 MeV.Comment: 4 pages, 3 figures. Proceedings of the workshop "Critical Stability of Few-Body Quantum Systems" 200

    Three-body halos. V. Computations of continuum spectra for Borromean nuclei

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    We solve the coordinate space Faddeev equations in the continuum. We employ hyperspherical coordinates and provide analytical expressions allowing easy computation of the effective potentials at distances much larger than the ranges of the interactions where only s-waves in the different Jacobi coordinates couple. Realistic computations are carried out for the Borromean halo nuclei 6He (n+n+\alpha) for J\pi = 0+-, 1+-, 2+- and 11Li (n+n+9Li) for (1/2)+-, (3/2)+-, (5/2)+-. Ground state properties, strength functions, Coulomb dissociation cross sections, phase shifts, complex S-matrix poles are computed and compared to available experimental data. We find enhancements of the strength functions at low energies and a number of low-lying S-matrix poles.Comment: 35 pages, 14 figure
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