Classical gravitational spin-spin interaction

I obtain an exact, axially symmetric, stationary solution of Einstein's equations for two massless spinning particles. The term representing the spin-spin interaction agrees with recently published approximate work. The spin-spin force appears to be proportional to the inverse fourth power of the coordinate distance between the particles.Comment: six pages, no figures, journal ref:accepted for Classical and Quantum Gravit

A Massively Parallel MIMD Implemented by SIMD Hardware?

Both conventional wisdom and engineering practice hold that a massively parallel MIMD machine should be constructed using a large number of independent processors and an asynchronous interconnection network. In this paper, we suggest that it may be beneficial to implement a massively parallel MIMD using microcode on a massively parallel SIMD microengine; the synchronous nature of the system allows much higher performance to be obtained with simpler hardware. The primary disadvantage is simply that the SIMD microengine must serialize execution of different types of instructions - but again the static nature of the machine allows various optimizations that can minimize this detrimental effect. In addition to presenting the theory behind construction of efficient MIMD machines using SIMD microengines, this paper discusses how the techniques were applied to create a 16,384- processor shared memory barrier MIMD using a SIMD MasPar MP-1. Both the MIMD structure and benchmark results are presented. Even though the MasPar hardware is not ideal for implementing a MIMD and our microinterpreter was written in a high-level language (MPL), peak MIMD performance was 280 MFLOPS as compared to 1.2 GFLOPS for the native SIMD instruction set. Of course, comparing peak speeds is of dubious value; hence, we have also included a number of more realistic benchmark results

National Transonic Facility: A review of the operational plan

The proposed National Transonic Facility (NTF) operational plan is reviewed. The NTF will provide an aerodynamic test capability significantly exceeding that of other transonic regime wind tunnels now available. A limited number of academic research program that might use the NTF are suggested. It is concluded that the NTF operational plan is useful for management, technical, instrumentation, and model building techniques available in the specialized field of aerodynamic analysis and simulation. It is also suggested that NASA hold an annual conference to discuss wind tunnel research results and to report on developments that will further improve the utilization and cost effectiveness of the NTF and other wind tunnels

Satellite power system: Concept development and evaluation program. Volume 3: Power transmission and reception. Technical summary and assessment

Efforts in the DOE/NASA concept development and evaluation program are discussed for the solar power satellite power transmission and reception system. A technical summary is provided together with a summary of system assessment activities. System options and system definition drivers are described. Major system assessment activities were in support of the reference system definition, solid state system studies, critical technology supporting investigations, and various system and subsystem tradeoffs. These activities are described together with reference system updates and alternative concepts for each of the subsystem areas. Conclusions reached as a result of the numerous analytical and experimental evaluations are presented. Remaining issues for a possible follow-on program are identified

The structure of the QED-Vacuum and Electron-Positron Pair Production in Super-Intense, pulsed Laser Fields

We discuss electron-positron pair-production by super-intense, short laser pulses off the physical vacuum state locally deformed by (stripped) nuclei with large nuclear charges. Consequences of non-perturbative vacuum polarisation resulting from such a deformation are shortly broached. Production probabilities per pulse are calculated.Comment: 10 pages, 1 figure, submitted to Journal of Physics

First Experimental Observation of Superscars in a Pseudointegrable Barrier Billiard

With a perturbation body technique intensity distributions of the electric field strength in a flat microwave billiard with a barrier inside up to mode numbers as large as about 700 were measured. A method for the reconstruction of the amplitudes and phases of the electric field strength from those intensity distributions has been developed. Recently predicted superscars have been identified experimentally and - using the well known analogy between the electric field strength and the quantum mechanical wave function in a two-dimensional microwave billiard - their properties determined.Comment: 4 pages, 5 .eps figure

Encircling an Exceptional Point

We calculate analytically the geometric phases that the eigenvectors of a parametric dissipative two-state system described by a complex symmetric Hamiltonian pick up when an exceptional point (EP) is encircled. An EP is a parameter setting where the two eigenvalues and the corresponding eigenvectors of the Hamiltonian coalesce. We show that it can be encircled on a path along which the eigenvectors remain approximately real and discuss a microwave cavity experiment, where such an encircling of an EP was realized. Since the wavefunctions remain approximately real, they could be reconstructed from the nodal lines of the recorded spatial intensity distributions of the electric fields inside the resonator. We measured the geometric phases that occur when an EP is encircled four times and thus confirmed that for our system an EP is a branch point of fourth order.Comment: RevTex 4.0, four eps-figures (low resolution

Difficulty of elderly SCI subjects to translate motor recovery -"body function"- into activity of daily living

The objective of this retrospective analysis was to determine whether outcome of body functions and activities as well as length of stay of inpatient rehabilitation is related to age in patients with traumatic spinal cord injury (SCI). Data were collected from a European network of 17 SCI rehabilitation centers (EM-SCI) and 237 traumatic SCI subjects were included. Assessments were performed at one, six and twelve months after SCI. The measures analyzed were: motor score according to the American Spinal Injury Association, Spinal Cord Independence Measure (SCIM), gait speed and length of stay. Correlation analysis was applied to quantify the association between age and change in the outcome measures. A positive relationship was found between age and neurological recovery in both the first and second 6 month- period of assessment. A negative relationship was found between age and change in SCIM in the second six month period after SCI. A negative relationship between age and gait speed was observed in the first half year. Length of stay was not associated with age. It is concluded that age is an important determining factor for functional outcome after SCI and that elderly patients have difficulties in translating an improvement in neurological outcome into functional changes. Therefore, rehabilitation approaches should focus on functional training in elderly subjects