Land vehicle antennas for satellite mobile communications

The RF performance, size, pointing system, and cost were investigated concepts are: for a mechanically steered 1 x 4 tilted microstrip array, a mechanically steered fixed-beam conformal array, and an electronically steered conformal phased array. Emphasis is on the RF performance of the tilted 1 x 4 antenna array and methods for pointing the various antennas studied to a geosynchronous satellite. An updated version of satellite isolations in a two-satellite system is presented. Cost estimates for the antennas in quantities of 10,000 and 100,000 unites are summarized

Neutron Drops and Skyrme Energy-Density Functionals

The J$^{\pi}$=0$^+$ ground state of a drop of 8 neutrons and the lowest 1/2$^-$ and 3/2$^-$ states of 7-neutron drops, all in an external well, are computed accurately with variational and Green's function Monte Carlo methods for a Hamiltonian containing the Argonne $v_{18}$ two-nucleon and Urbana IX three-nucleon potentials. These states are also calculated using Skyrme-type energy-density functionals. Commonly used functionals overestimate the central density of these drops and the spin-orbit splitting of 7-neutron drops. Improvements in the functionals are suggested

An algal enzyme required for biosynthesis of the most abundant marine carotenoids.

Fucoxanthin and its derivatives are the main light-harvesting pigments in the photosynthetic apparatus of many chromalveolate algae and represent the most abundant carotenoids in the world's oceans, thus being major facilitators of marine primary production. A central step in fucoxanthin biosynthesis that has been elusive so far is the conversion of violaxanthin to neoxanthin. Here, we show that in chromalveolates, this reaction is catalyzed by violaxanthin de-epoxidase-like (VDL) proteins and that VDL is also involved in the formation of other light-harvesting carotenoids such as peridinin or vaucheriaxanthin. VDL is closely related to the photoprotective enzyme violaxanthin de-epoxidase that operates in plants and most algae, revealing that in major phyla of marine algae, an ancient gene duplication triggered the evolution of carotenoid functions beyond photoprotection toward light harvesting

Variational calculations of the Λ\Lambda-seperation energy of the Λ17_{\Lambda}^{17}O hypernucleus

Variational Monte Carlo calculations have been made for the $_{ \Lambda}^{17}$O hypernucleus using realistic two- and three-baryon interactions. A two pion exchange potential with spin- and space-exchange components is used for the $\Lambda$N potential. Three-body two-pion exchange and strongly repulsive dispersive $\Lambda$NN interactions are also included. The trial wave function is constructed from pair- and triplet-correlation operators acting on a single particle determinant. These operators consist of central, spin, isospin, tensor and three- baryon potential components. A cluster Monte Carlo method is developed for noncentral correlations and is used with up to four-baryon clusters in our calculations. The three-baryon $\Lambda$NN force is discussed.Comment: 24 pages, 2 figs available by fax., for publication in Phys. Rev.

Ground state correlations and mean-field in 16^{16}O

We use the coupled cluster expansion ($\exp(S)$ method) to generate the complete ground state correlations due to the NN interaction. Part of this procedure is the calculation of the two-body G matrix inside the nucleus in which it is being used. This formalism is being applied to $^{16}O$ in a configuration space of 50 $\hbar\omega$. The resulting ground state wave function is used to calculate the binding energy and one- and two-body densities for the ground state of $^{16}O$.Comment: 9 pages, 9 figures, LaTe

Momentum and Energy Distributions of Nucleons in Finite Nuclei due to Short-Range Correlations

The influence of short-range correlations on the momentum and energy distribution of nucleons in nuclei is evaluated assuming a realistic meson-exchange potential for the nucleon-nucleon interaction. Using the Green-function approach the calculations are performed directly for the finite nucleus $^{16}$O avoiding the local density approximation and its reference to studies of infinite nuclear matter. The nucleon-nucleon correlations induced by the short-range and tensor components of the interaction yield an enhancement of the momentum distribution at high momenta as compared to the Hartree-Fock description. These high-momentum components should be observed mainly in nucleon knockout reactions like $(e,e'p)$ leaving the final nucleus in a state of high excitation energy. Our analysis also demonstrates that non-negligible contributions to the momentum distribution should be found in partial waves which are unoccupied in the simple shell-model. The treatment of correlations beyond the Brueckner-Hartree-Fock approximation also yields an improvement for the calculated ground-state properties.Comment: 12 pages RevTeX, 7 figures postscript files appende

Lattice Simulations for Light Nuclei: Chiral Effective Field Theory at Leading Order

We discuss lattice simulations of light nuclei at leading order in chiral effective field theory. Using lattice pion fields and auxiliary fields, we include the physics of instantaneous one-pion exchange and the leading-order S-wave contact interactions. We also consider higher-derivative contact interactions which adjust the S-wave scattering amplitude at higher momenta. By construction our lattice path integral is positive definite in the limit of exact Wigner SU(4) symmetry for any even number of nucleons. This SU(4) positivity and the approximate SU(4) symmetry of the low-energy interactions play an important role in suppressing sign and phase oscillations in Monte Carlo simulations. We assess the computational scaling of the lattice algorithm for light nuclei with up to eight nucleons and analyze in detail calculations of the deuteron, triton, and helium-4.Comment: 44 pages, 15 figure

Time-Dependent Current Partition in Mesoscopic Conductors

The currents at the terminals of a mesoscopic conductor are evaluated in the presence of slowly oscillating potentials applied to the contacts of the sample. The need to find a charge and current conserving solution to this dynamic current partition problem is emphasized. We present results for the electro-chemical admittance describing the long range Coulomb interaction in a Hartree approach. For multiply connected samples we discuss the symmetry of the admittance under reversal of an Aharonov-Bohm flux.Comment: 22 pages, 3 figures upon request, IBM RC 1971