Some partial-unit-memory convolutional codes

The results of a study on a class of error correcting codes called partial unit memory (PUM) codes are presented. This class of codes, though not entirely new, has until now remained relatively unexplored. The possibility of using the well developed theory of block codes to construct a large family of promising PUM codes is shown. The performance of several specific PUM codes are compared with that of the Voyager standard (2, 1, 6) convolutional code. It was found that these codes can outperform the Voyager code with little or no increase in decoder complexity. This suggests that there may very well be PUM codes that can be used for deep space telemetry that offer both increased performance and decreased implementational complexity over current coding systems

Carrier extraction circuit

Feedback loop extracts demodulated reference signals from IF input and feeds signal back to demodulator. Since reference signal is extracted directly from carrier, no separate reference need be transmitted. Circuit obtains coherent carrier from balanced or unbalanced four-phase signal of varying characteristics

A new look at the problem of gauge invariance in quantum field theory

Quantum field theory is assumed to be gauge invariant. However it is well known that when certain quantities are calculated using perturbation theory the results are not gauge invariant. The non-gauge invariant terms have to be removed in order to obtain a physically correct result. In this paper we will examine this problem and determine why a theory that is supposed to be gauge invariant produces non-gauge invariant results.Comment: Accepted by Physica Scripta. 27 page

Chaotic diffusion of particles with finite mass in oscillating convection flows

Deterministic diffusion in temporally oscillating convection is studied for particles with finite mass. The particles are assumed to obey a simple dissipative dynamical system and the particle diffusion is induced by the strange attractor. The diffusion constants are numerically calculated for convection models with free and rigid boundary conditions.Comment: 5 figure

Using handheld pocket computers in a wireless telemedicine system

Objectives: To see if senior emergency nurse practitioners can provide support to inexperienced ones in a Minor Injuries Unit by using a wireless LAN system of telemedicine transmitting images to a PDA when they were on duty. In addition, whether such a system could be sufficiently accurate to make clinical diagnoses with a high level of diagnostic confidence. This would permit an overall lower grade of nurse to be employed to manage most of the cases as they arrive with a proportionate lowering of costs. Methods: The wireless LAN equipment could roam in the Minor Injuries Unit and the experienced emergency Nurse practitioners could be at home, shopping or even at a considerable distance from the centre. Thirty pictorial images of patients who had been sent to the Review Clinic were transmitted to a PDA various distances of one to sixteen miles from the centre. Two senior emergency nurse practitioners viewed the images and opined on the diagnosis, their degree of confidence in the diagnosis and their opinion of the quality of the image. Results: the images of patients were sharp, clear, and of diagnostic quality. The image quality was only uncertain, as was the level of confidence of the diagnosis if the patient was very dark skinned. Conclusions: The wireless LAN system works with a remote PDA in this clinical situation. However there are question marks over the availability of enough experienced emergency nurse practitioners to staff a service that provides senior cover for longer parts of the day and at weekends

Some new results concerning the vacuum in Dirac Hole Theory

In Dirac's hole theory the vacuum state is generally believed to be the state of minimum energy. It will be shown that this is not, in fact, the case and that there must exist states in hole theory with less energy than the vacuum state. It will be shown that energy can be extracted from the hole theory vacuum state through the application of an electric field.Comment: Accepted by Physica Scripta, 19 page

Space and surface power for the space exploration initiative: Results from project outreach

The analysis and evaluations of the Space and Surface Power panel, one of eight panels created by RAND to screen and analyze submissions to the Space Exploration Initiative (SEI) Outreach Program, is documented. In addition to managing and evaluating the responses, or submissions, to this public outreach program, RAND conducted its own analysis and evaluation relevent to SEI mission concepts, systems, and technologies. The Power panel screened and analyzed submissions for which a substantial portion of the concepts involved power generation sources, transmission, distribution, thermal management, and handling of power (including conditioning, conversion, packaging, and enhancements in system components). A background discussion of the areas the Power panel covered and the issues the reviewers considered pertinent to the analysis of power submissions are presented. An overview of each of the highest-ranked submissions and then a discussion of these submissions is presented. The results of the analysis is presented

Coherent pairing states for the Hubbard model

We consider the Hubbard model and its extensions on bipartite lattices. We define a dynamical group based on the $\eta$-pairing operators introduced by C.N.Yang, and define coherent pairing states, which are combinations of eigenfunctions of $\eta$-operators. These states permit exact calculations of numerous physical properties of the system, including energy, various fluctuations and correlation functions, including pairing ODLRO to all orders. This approach is complementary to BCS, in that these are superconducting coherent states associated with the exact model, although they are not eigenstates of the Hamiltonian.Comment: 5 pages, RevTe