Design of a fault tolerant airborne digital computer. Volume 2: Computational requirements and technology

This final report summarizes the work on the design of a fault tolerant digital computer for aircraft. Volume 2 is composed of two parts. Part 1 is concerned with the computational requirements associated with an advanced commercial aircraft. Part 2 reviews the technology that will be available for the implementation of the computer in the 1975-1985 period. With regard to the computation task 26 computations have been categorized according to computational load, memory requirements, criticality, permitted down-time, and the need to save data in order to effect a roll-back. The technology part stresses the impact of large scale integration (LSI) on the realization of logic and memory. Also considered was module interconnection possibilities so as to minimize fault propagation

Soft X-ray seeding studies for the SLAC Linac Coherent Light Source II

We present the results from studies of soft X-ray seeding options for the LCLS-II X-ray free electron laser (FEL) at SLAC. The LCLS-II will use superconducting accelerator technology to produce X-ray pulses at up to 1 MHz repetition rate using 4 GeV electron beams. If properly seeded, these pulses will be nearly fully coherent, and highly stable in photon energy, bandwidth, and intensity, thus enabling unique experiments with intense high-resolution soft X-rays. Given the expected electron beam parameters from start to end simulations and predicted FEL performance, our studies reveal echo enabled harmonic generation (EEHG) and soft X-ray self-seeding (SXRSS) as promising and complementary seeding methods. We find that SXRSS has the advantage of simplicity and will deliver 5-35 times higher spectral brightness than EEHG in the 1-2 nm range, but lacks some of the potential for phase-stable multipulse and multicolor FEL operations enabled by external laser seeding with EEHG

Equidistribution Rates, Closed String Amplitudes, and the Riemann Hypothesis

We study asymptotic relations connecting unipotent averages of $Sp(2g,\mathbb{Z})$ automorphic forms to their integrals over the moduli space of principally polarized abelian varieties. We obtain reformulations of the Riemann hypothesis as a class of problems concerning the computation of the equidistribution convergence rate in those asymptotic relations. We discuss applications of our results to closed string amplitudes. Remarkably, the Riemann hypothesis can be rephrased in terms of ultraviolet relations occurring in perturbative closed string theory.Comment: 15 page

Symposium: THE MULTINATIONAL ENTERPRISE AS GLOBAL CORPORATE CITIZEN

The word globalization finds its way into many commentaries these days, in different ways and different connotations. Sometimes it is thought to be beneficial, and sometimes it\u27s thought to be harmful. We have here today four people highly qualified to talk about this topic. The focus on the multinational enterprise, which is one of the terms that\u27s used for a company that does business in many jurisdictions, is the focus of today\u27s discussion, and whether and how multinational enterprises function as global corporate citizens

VLBI for Gravity Probe B. VII. The Evolution of the Radio Structure of IM Pegasi

We present measurements of the total radio flux density as well as very-long-baseline interferometry (VLBI) images of the star, IM Pegasi, which was used as the guide star for the NASA/Stanford relativity mission Gravity Probe B. We obtained flux densities and images from 35 sessions of observations at 8.4 GHz (wavelength = 3.6 cm) between 1997 January and 2005 July. The observations were accurately phase-referenced to several extragalactic reference sources, and we present the images in a star-centered frame, aligned by the position of the star as derived from our fits to its orbital motion, parallax, and proper motion. Both the flux density and the morphology of IM Peg are variable. For most sessions, the emission region has a single-peaked structure, but 25% of the time, we observed a two-peaked (and on one occasion perhaps a three-peaked) structure. On average, the emission region is elongated by 1.4 +- 0.4 mas (FWHM), with the average direction of elongation being close to that of the sky projection of the orbit normal. The average length of the emission region is approximately equal to the diameter of the primary star. No significant correlation with the orbital phase is found for either the flux density or the direction of elongation, and no preference for any particular longitude on the star is shown by the emission region.Astronom

Antiresonances in Molecular Wires

We present analytic and numerical studies based on Landauer theory of conductance antiresonances of molecular wires. Our analytic treatment is a solution of the Lippmann-Schwinger equation for the wire that includes the effects of the non-orthogonality of the atomic orbitals on different atoms exactly. The problem of non-orthogonality is treated by solving the transport problem in a new Hilbert space which is spanned by an orthogonal basis. An expression is derived for the energies at which antiresonances should occur for a molecular wire connected to a pair of single-channel 1D leads. From this expression we identify two distinct mechanisms that give rise to antiresonances under different circumstances. The exact treatment of non-orthogonality in the theory is found to be necessary to obtain reliable results. Our numerical simulations extend this work to multichannel leads and to molecular wires connected to 3D metallic nanocontacts. They demonstrate that our analytic results also provide a good description of these more complicated systems provided that certain well-defined conditions are met. These calculations suggest that antiresonances should be experimentally observable in the differential conductance of molecular wires of certain types.Comment: 22 pages, 5 figure