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Search Results: 1 - 10 of 257911 matches for " W. D. Phillips "
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Relative Competitiveness of Nimblewill (Muhlenbergia schreberi) with Tall Fescues and Kentucky Bluegrass  [PDF]
Pedro V. D. Moraes, Willian W. Witt, Timothy D. Phillips, Patricia Rossi, Luis E. Panozzo
American Journal of Plant Sciences (AJPS) , 2014, DOI: 10.4236/ajps.2014.526395
Abstract: Nimblewill (Muhlenbergia schreberi) is a warm-season perennial grass (weed) native to the United States and Canada with low palatability. This species is dominant in many horse pastures in which bluegrass (Poa pratensis) is the primary forage. Tall fescues infected with endophyte fungae gives tall fescue plants greater competitividade ability and enviromental stress tolerance than their noninfected counterparts. The purpose of this study was to compare the relative competitiveness of nimblewill with bluegrass and tall fescues (Lolium arundinaceum) with or without endophytic fungi (strain AR584) through experiments using a replacement series design. Replacement series experiments were conducted in pots to evaluate the growth of species in a pure stand and in a mix stand with variables rates. Species competitiveness was evaluated based on the relative yield and relative yield total (and competitiveness index) of the dry weight of shoots from species grown together. Nimblewill was found to be more competitive than bluegrass, and all tall fescues were more competitive than nimblewill. Our results demonstrated that the presence of endophytes in three different tall fescues did not alter the competitiveness of these fescues with nimblewill, but the tall fescue Kentucky 31 was more competitive between tall fescues. Based on our finding, we concluded that fescues are recommended, especially without the endophytic fungi to suppress nimblewill in implantation of pastures to horses.
Electric properties of the Beryllium-11 system in Halo EFT
H. -W. Hammer,D. R. Phillips
Physics , 2011, DOI: 10.1016/j.nuclphysa.2011.06.028
Abstract: We compute E1 transitions and electric radii in the Beryllium-11 nucleus using an effective field theory that exploits the separation of scales in this halo system. We fix the leading-order parameters of the EFT from measured data on the 1/2+ and 1/2- levels in Be-11 and the B(E1) strength for the transition between them. We then obtain predictions for the B(E1) strength for Coulomb dissociation of the Be-11 nucleus to the continuum. We also compute the charge radii of the 1/2+ and 1/2- states. Agreement with experiment within the expected accuracy of a leading-order computation in this EFT is obtained. We also discuss how next-to-leading-order (NLO) corrections involving both s-wave and p-wave neutron-Be-10 interactions affect our results, and display the NLO predictions for quantities which are free of additional short-distance operators at this order. Information on neutron-Be-10 scattering in the relevant channels is inferred.
Pion-mass dependence of three-nucleon observables
Hammer, H. -W.;Phillips, D. R.;Platter, L.
High Energy Physics - Phenomenology , 2007, DOI: 10.1140/epja/i2007-10380-y
Abstract: We use an effective field theory (EFT) which contains only short-range interactions to study the dependence of a variety of three-nucleon observables on the pion mass. The pion-mass dependence of input quantities in our ``pionless'' EFT is obtained from a recent chiral EFT calculation. To the order we work at, these quantities are the 1S0 scattering length and effective range, the deuteron binding energy, the 3S1 effective range, and the binding energy of one three-nucleon bound state. The chiral EFT input we use has the inverse 3S1 and 1S0 scattering lengths vanishing at mpi_c=197.8577 MeV. At this ``critical'' pion mass, the triton has infinitely many excited states with an accumulation point at the three-nucleon threshold. We compute the binding energies of these states up to next-to-next-to-leading order in the pionless EFT and study the convergence pattern of the EFT in the vicinity of the critical pion mass. Furthermore, we use the pionless EFT to predict how doublet and quartet nd scattering lengths depend on mpi in the region between the physical pion mass and mpi=mpi_c.
Coherent Spin Polarization in an AC-Driven Mesoscopic Device
Asham M. D.,Zein W. A.,Phillips A. H.
Progress in Physics , 2012,
Abstract: The spin transport characteristics through a mesoscopic device are investigated under the e ect of an AC- eld. This device consists of two-diluted magnetic semiconductor (DMS) leads and a nonmagnetic semiconducting quantum dot. The conductance for both spin parallel and antiparallel alignment in the two DMS leads is deduced. Thecorresponding equations for giant magnetoresistance (GMR) and spin polarization (SP) are also deduced. Calculations show an oscillatory behavior of the present studied parameters. These oscillations are due to the coupling of photon energy and spin-up & spin-down subbands and also due to Fano-resonance. This research work is very important for spintronic devices.
Electromagnetic properties of the Beryllium-11 nucleus in Halo EFT
Phillips D.R.,Hammer H.-W.
EPJ Web of Conferences , 2010, DOI: 10.1051/epjconf/20100306002
Abstract: We compute electromagnetic properties of the Beryllium-11 nucleus using an e ective eld theory that exploits the separation of scales in this halo system. We x the parameters of the EFT from measured data on levels and scattering lengths in the 10Be plus neutron system. We then obtain predictions for the B(E1) strength of the 1/2+ to 1/2 transition in the 11Be nucleus. We also compute the charge radius of the ground state of 11Be. Agreement with experiment within the expected accuracy of a leading-order computation in this EFT is obtained. We also indicate how higher-order corrections that a ect both s-wave and p-wave 10 Be-neutron interactions will a ect our results.
Working Group Summary: Chiral Dynamics in Few-Nucleon Systems
H. -W. Hammer,N. Kalantar-Nayestanaki,D. R. Phillips
Physics , 2006,
Abstract: We summarize the findings of our Working Group, which discussed progress in the understanding of Chiral Dynamics in the A=2, 3, and 4 systems over the last three years. We also identify key unresolved theoretical and experimental questions in this field.
Condensate fraction in a 2D Bose gas measured across the Mott-insulator transition
I. B. Spielman,W. D. Phillips,J. V. Porto
Physics , 2008, DOI: 10.1103/PhysRevLett.100.120402
Abstract: We realize a single-band 2D Bose-Hubbard system with Rb atoms in an optical lattice and measure the condensate fraction as a function of lattice depth, crossing from the superfluid to the Mott-insulating phase. We quantitatively identify the location of the superfluid to normal transition by observing when the condensed fraction vanishes. Our measurement agrees with recent quantum Monte Carlo calculations for a finite-sized 2D system to within experimental uncertainty.
The Mott insulator transition in two dimensions
I. B. Spielman,W. D. Phillips,J. V. Porto
Physics , 2006, DOI: 10.1103/PhysRevLett.98.080404
Abstract: Cold atoms confined in periodic potentials are remarkably versatile quantum systems for implementing simple models prevalent in condensed matter theory. In the current experiment, we realize the 2D Bose-Hubbard model by loading a Bose-Einstein condensate into an optical lattice, and we study the resulting Mott insulating state (a phase of matter in which atoms are localized on specific lattice sites). We measure momentum distributions which agree quantitatively with theory (no adjustable parameters). We also study correlations in atom shot nose and observe a pronounced dependence on the lattice depth, this dependence indicates geometric effects to first order and suggests deviations due to higher order corrections.
Much Ado about Zeros: The Luttinger Surface and Mottness
Tudor D. Stanescu,Philip W. Phillips,Ting-Pong Choy
Physics , 2006, DOI: 10.1103/PhysRevB.75.104503
Abstract: We prove that the Mott insulating state is characterized by a divergence of the electron self energy at well-defined values of momenta in the first Brillouin zone. When particle-hole symmetry is present, the divergence obtains at the momenta of the Fermi surface for the corresponding non-interacting system. Such a divergence gives rise to a surface of zeros (the Luttinger surface) of the single-particle Green function and offers a single unifying principle of Mottness from which pseudogap phenomena, spectral weight transfer, and broad spectral features emerge in doped Mott insulators. We also show that only when particle-hole symmetry is present does the volume of the zero surface equal the particle density. We identify that the general breakdown of Luttinger's theorem in a Mott insulator arises from the breakdown of a perturbative expansion for the self energy in the single-particle Green function around the non-interacting limit. A modified version of Luttinger's theorem is derived for special cases.
Five dimensional supergravity in N = 1 superspace
W. D. Linch III,Markus A. Luty,J. Phillips
Physics , 2002, DOI: 10.1103/PhysRevD.68.025008
Abstract: We give a formulation of linearized minimal 5-dimensional supergravity in N = 1 superspace. Infinitesimal local 5D diffeomorphisms, local 5D Lorentz transformations, and local 5D supersymmetry are all realized as off-shell superfield transformations. Compactification on an S^1 / Z_2 orbifold and couplings to brane-localized supermultiplets are very simple in this formalism. We use this to show that 5-dimensional supergravity can naturally generate mu and B mu terms of the correct size in gaugino- or radion-mediated supersymmetry breaking. We also include a self-contained review of linearized minimal 4D supergravity in superspace.
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