Magnetic Phase Diagram of the Ferromagnetically Stacked Triangular Ising Antiferromagnet

Histogram Monte-Carlo simulation results are presented for the magnetic-field -- temperature phase diagram of the Ising model on a stacked triangular lattice with antiferromagnetic intraplane and ferromagnetic interplane interactions. Finite-size scaling results for this frustrated system at three points along the paramagnetic transition boundary are presented which strongly suggest a line of triciritcal points at low field and a first-order transition line at higher fields. These results are compared with the corresponding phase diagrams from conventional mean-field theory as well as from the Monte Carlo mean-field calculations of Netz and Berker [Phys. Rev. Lett. {\bf 66}, 377 (1991)].Comment: 6 pages (RevTex 3.0), 8 figures available upon reques

Two Epistemic Issues for a Narrative Argument Structure

The transcendental approach to understanding narrative argument derives from the idea that for any believable fictional narrative, we can ask—what principles or generalizations would have to be true of human nature in order for the narrative to be believable? I address two key issues: whether only realistic or realist fictional narratives are believable, and how could it be established that we have an intuitive, mostly veridical grasp of human nature that grounds believability

Can Cogency Vanish?

This paper considers whether universally—for all (known) rational beings—an argument scheme or pattern can go from being cogent (well-reasoned) to fallacious. This question has previously received little attention, despite the centrality of the concepts of cogency, scheme, and fallaciousness. I argue that cogency has vanished in this way for the following scheme, a common type of impersonal means-end reasoning: X is needed as a basic necessity or protection of human lives, therefore, X ought to be secured if possible. As it stands (with no further elaboration), this scheme is committed to the assumption that the greater the number of human lives, the better. Although this assumption may have been indisputable previously, it is clearly disputable now. It is a fallacy or non sequitur to make a clearly disputable assumption without providing any justification. Although this topic raises critical issues for practically every discipline, my primary focus is on logical (as opposed to empirical or ethical) aspects of the case, and on implications for practical and theoretical logic. I conclude that the profile of vanishing cogency of the scheme may be unique and is determined by a peculiar combination of contingent universality and changing conditions

Cascading a systolic array and a feedforward neural network for navigation and obstacle avoidance using potential fields

A technique is developed for vehicle navigation and control in the presence of obstacles. A potential function was devised that peaks at the surface of obstacles and has its minimum at the proper vehicle destination. This function is computed using a systolic array and is guaranteed not to have local minima. A feedfoward neural network is then used to control the steering of the vehicle using local potential field information. In this case, the vehicle is a trailer truck backing up. Previous work has demonstrated the capability of a neural network to control steering of such a trailer truck backing to a loading platform, but without obstacles. Now, the neural network was able to learn to navigate a trailer truck around obstacles while backing toward its destination. The network is trained in an obstacle free space to follow the negative gradient of the field, after which the network is able to control and navigate the truck to its target destination in a space of obstacles which may be stationary or movable

Magnetic Phase Diagram of the Ferromagnetically Stacked Triangular XY Antiferromagnet: A Finite-Size Scaling Study

Histogram Monte-Carlo simulation results are presented for the magnetic-field -- temperature phase diagram of the XY model on a stacked triangular lattice with antiferromagnetic intraplane and ferromagnetic interplane interactions. Finite-size scaling results at the various transition boundaries are consistent with expectations based on symmetry arguments. Although a molecular-field treatment of the Hamiltonian fails to reproduce the correct structure for the phase diagram, it is demonstrated that a phenomenological Landau-type free-energy model contains all the esstential features. These results serve to complement and extend our earlier work [Phys. Rev. B {\bf 48}, 3840 (1993)].Comment: 5 pages (RevTex 3.0), 6 figures available upon request, CRPS 93-

Status of research into lightning effects on aircraft

Developments in aircraft lightning protection since 1938 are reviewed. Potential lightning problems resulting from present trends toward the use of electronic controls and composite structures are discussed, along with presently available lightning test procedures for problem assessment. The validity of some procedures is being questioned because of pessimistic results and design implications. An in-flight measurement program is needed to provide statistics on lightning severity at flight altitudes and to enable more realistic tests, and operators are urged to supply researchers with more details on electronic components damaged by lightning strikes. A need for review of certain aspects of fuel system vulnerability is indicated by several recent accidents, and specific areas for examination are identified. New educational materials and standardization activities are also noted

Mean-field transfer-matrix study of the magnetic phase diagram of CsNiF3_{\bf 3}

A method for treating ferromagnetic chains coupled with antiferromagnetic interactions on an hexagonal lattice is presented in this paper. The solution of the $1D$ part of the problem is obtained by classical transfer-matrix while the coupling between the chains is processed by mean-field theory. This method is applied with success to the phase diagram and angular dependence of the critical field of CsNiF$_3$. Results concerning the general influence of single-ion anisotropy on the magnetic ordering of such systems are also presented.Comment: J1K 2R1 14 pages (RevTex 3.0 preprint), 7 Postscript figures uuencoded at the end, Report# CRPS-94-2

Investigation of severe lightning strike incidents to two USAF F-106A aircraft

The results of the inspection and analysis of two F-106A aircraft that were struck by separate lightning strikes within a few minutes of each other are presented. Each aircraft sustained severe lightning strikes to the pitot booms, resulting in extensive damage to the pitot heater power harness, number 8 ground wire, and lightning suppressors, but there was no damage to either aircraft's electrical or avionic systems. A simulated lightning current of 226 kA and 3.8 million A(2)*S was required to reproduce the damage to the ground wires in the radomes. Photographs and detailed assessments of the damage are included

Two neural network algorithms for designing optimal terminal controllers with open final time

Multilayer neural networks, trained by the backpropagation through time algorithm (BPTT), have been used successfully as state-feedback controllers for nonlinear terminal control problems. Current BPTT techniques, however, are not able to deal systematically with open final-time situations such as minimum-time problems. Two approaches which extend BPTT to open final-time problems are presented. In the first, a neural network learns a mapping from initial-state to time-to-go. In the second, the optimal number of steps for each trial run is found using a line-search. Both methods are derived using Lagrange multiplier techniques. This theoretical framework is used to demonstrate that the derived algorithms are direct extensions of forward/backward sweep methods used in N-stage optimal control. The two algorithms are tested on a Zermelo problem and the resulting trajectories compare favorably to optimal control results