Electronics systems test laboratory testing of shuttle communications systems

Shuttle communications and tracking systems space to space and space to ground compatibility and performance evaluations are conducted in the NASA Johnson Space Center Electronics Systems Test Laboratory (ESTL). This evaluation is accomplished through systems verification/certification tests using orbiter communications hardware in conjunction with other shuttle communications and tracking external elements to evaluate end to end system compatibility and to verify/certify that overall system performance meets program requirements before manned flight usage. In this role, the ESTL serves as a multielement major ground test facility. The ESTL capability and program concept are discussed. The system test philosophy for the complex communications channels is described in terms of the major phases. Results of space to space and space to ground systems tests are presented. Several examples of the ESTL's unique capabilities to locate and help resolve potential problems are discussed in detail

Positronic complexes with unnatural parity

The structure of the unnatural parity states of PsH, LiPs, NaPs and KPs are investigated with the configuration interaction and stochastic variational methods. The binding energies (in hartree) are found to be 8.17x10-4, 4.42x10-4, 15.14x10-4 and 21.80x10-4 respectively. These states are constructed by first coupling the two electrons into a configuration which is predominantly 3Pe, and then adding a p-wave positron. All the active particles are in states in which the relative angular momentum between any pair of particles is at least L = 1. The LiPs state is Borromean since there are no 3-body bound subsystems (of the correct symmetry) of the (Li+, e-, e-, e+) particles that make up the system. The dominant decay mode of these states will be radiative decay into a configuration that autoionizes or undergoes positron annihilation.Comment: 10 pages RevTeX, 6 figures, in press Phys.Rev.

Discharge-generated electrical fields and electrical tree structures

The discharge-avalanche (D-A) model for electrical tree propagation in polymers is founded entirely upon basic physical concepts. Electrical discharges in an existing tree structure are taken to raise the electrical field in the polymer both along the discharge path and particularly at the tree tips. As a result of the field increase, electron multiplication avalanches occur within the polymer causing damage, possibly through ionisation of polymer molecules, which is accumulated over a period of thousands (or more) cycles and eventually leads to a tree extension of limited size. The assumption that the damage produced in an avalanche is proportional to the number of ionisations allows the model to be expressed quantitatively in terms of material properties: such as the ionisation potential, I; the impact-ionisation length parameter λ; the critical number of ionisations for tree extension Nc; discharge features such as the number of 1-electron initiated avalanches per half cycle, Nb ; and the potential difference ΔV between the start and end of the avalanche over a distance Lb

Memorandum for the National Security Council

Memorandum for the National Security Council regarding attached paper discussing objectives and problems and policy solution in the Inter-American Region

Alpha-particle-induced breakup of the deuteron

Alpha-particle-induced deuteron breakup reactions have been studied in single-counter measurements at incident alpha-particle energies of 41.6 and 29.3 MeV. Simultaneous differential and total cross-section measurements have been carried out on protons, deuterons, and alpha particles. Unambiguous evidence for final-state resonance effects in the alpha-nucleon interactions have been obtained, particularly from the proton energy spectra; the p3/2 alpha-nucleon resonances corresponding to the He5 and Li5 ground states play important roles. As anticipated, phase-space-factor and zero-range Born-approximation calculations failed to reproduce the observed energy spectra. A more exact analysis which explicitly includes the alpha-nucleon interactions, represented by Gammel-Thaler phenomenological potentials, does provide good agreement with the experimental results both in spectrum shape and in total breakup cross section

Large dimension Configuration Interaction calculations of positron binding to the group II atoms

The Configuration Interaction (CI) method is applied to the calculation of the structures of a number of positron binding systems, including e+Be, e+Mg, e+Ca and e+Sr. These calculations were carried out in orbital spaces containing about 200 electron and 200 positron orbitals up to l = 12. Despite the very large dimensions, the binding energy and annihilation rate converge slowly with l, and the final values do contain an appreciable correction obtained by extrapolating the calculation to the l to infinity limit. The binding energies were 0.00317 hartree for e+Be, 0.0170 hartree for e+Mg, 0.0189 hartree for e+Ca, and 0.0131 hartree for e+Sr.Comment: 13 pages, no figs, revtex format, Submitted to PhysRev

Models of helically symmetric binary systems

Results from helically symmetric scalar field models and first results from a convergent helically symmetric binary neutron star code are reported here; these are models stationary in the rotating frame of a source with constant angular velocity omega. In the scalar field models and the neutron star code, helical symmetry leads to a system of mixed elliptic-hyperbolic character. The scalar field models involve nonlinear terms that mimic nonlinear terms of the Einstein equation. Convergence is strikingly different for different signs of each nonlinear term; it is typically insensitive to the iterative method used; and it improves with an outer boundary in the near zone. In the neutron star code, one has no control on the sign of the source, and convergence has been achieved only for an outer boundary less than approximately 1 wavelength from the source or for a code that imposes helical symmetry only inside a near zone of that size. The inaccuracy of helically symmetric solutions with appropriate boundary conditions should be comparable to the inaccuracy of a waveless formalism that neglects gravitational waves; and the (near zone) solutions we obtain for waveless and helically symmetric BNS codes with the same boundary conditions nearly coincide.Comment: 19 pages, 7 figures. Expanded version of article to be published in Class. Quantum Grav. special issue on Numerical Relativit

Kinematic Effects of Tidal Interaction on Galaxy Rotation Curves

We use self-consistent N-body models, in conjunction with models of test particles moving in galaxy potentials, to explore the initial effects of interactions on the rotation curves of spiral galaxies. Using nearly self-consistent disk/bulge/halo galaxy models (Kuijken & Dubinski 1995), we simulate the first pass of galaxies on nearly parabolic orbits; we vary orbit inclinations, galaxy halo masses and impact parameters. For each simulation, we mimic observed rotation curves of the model galaxies. Transient interaction-induced features of the curves include distinctly rising or falling profiles at large radii and pronounced bumps in the central regions. Remarkably similar features occur in our statistical sample of optical emission-line rotation curves of spiral galaxies in tight pairs and n-tuples.Comment: 9 pages, 2 figures, accepted for publication in ApJ Letter

Functional mapping of stimulus colour in human subjects suffering a central visual defect

The multiple maps of the visual field found in the striate and the pre-striate cortex of the macaque exhibit selective responsiveness to different stimulus parameters (Zeki, 1978, 1980). Evidence for such organization in man is derived primarily from selective losses of visual function associated with disturbance of the central pathways. We present data for a single subject, M. W., who has normal achromatic vision but exhibits grossly abnormal responses to coloured and particularly red stumuli ..