Arc-cathode interaction study

Insufficient electrode life and uncertainties in that life are major problems hampering the development in many plasma application areas which make use of plasma torches, arc heaters, and arc jet thrusters. In spite of a considerable amount of work published dealing with arc-cathode phenomena, our present understanding is still incomplete because different physical phenomena dominate for different combinations of experimental parameters. The objective of our present research project is to gain a better understanding of the behavior of arc-cathode surface interaction over a wide range of parameters, and furthermore to develop guidelines for better thermal design of the electrode and the selection of materials. This report will present the research results and progress obtained on the arc-cathode interaction studies at the University of Minnesota. It includes results which have been obtained under programs other than the NASA funded program. Some of the results have been submitted in an informal interim progress report, and all of the results have been presented in a seminar during a visit to the NASA Lewis Research Center on October 16, 1992

[Develop and Evaluate the Performance of Single and Multi-Specimen Respirometers.] Technical Report, 4 Nov. 1968 - 4 Feb. 1969

Development and performance of respirometers for biorhythmic studies of gravity effect

Personhood and neuroscience: Naturalizing or nihilating?

Personhood is a foundational concept in ethics, yet defining criteria have been elusive. In this article we summarize attempts to define personhood in psychological and neurological terms and conclude that none manage to be both specific and non-arbitrary. We propose that this is because the concept does not correspond to any real category of objects in the world. Rather, it is the product of an evolved brain system that develops innately and projects itself automatically and irrepressibly onto the world whenever triggered by stimulus features such as a human-like face, body, or contingent patterns of behavior. We review the evidence for the existence of an autonomous person network in the brain and discuss its implications for the field of ethics and for the implicit morality of everyday behavior

Response to Open Peer Commentaries on Personhood and Neuroscience: Naturalizing or Nihilating? : Getting Personal

Personhood is a foundational concept in ethics, yet defining criteria have been elusive. In this article we summarize attempts to define personhood in psychological and neurological terms and conclude that none manage to be both specific and non-arbitrary. We propose that this is because the concept does not correspond to any real category of objects in the world. Rather, it is the product of an evolved brain system that develops innately and projects itself automatically and irrepressibly onto the world whenever triggered by stimulus features such as a human-like face, body, or contingent patterns of behavior. We review the evidence for the existence of an autonomous person network in the brain and discuss its implications for the field of ethics and for the implicit morality of everyday behavior

Arc electrode interaction study

The project consisted of two parts: (1) the cathode interaction studies which were a continuation of previous work and had the objective of increasing our understanding of the microscopic phenomena controlling cathode erosion in arc jet thrusters, and (2) the studies of the anode attachment in arc jet thrusters. The cathode interaction studies consisted of (1) a continuation of some modeling work in which the previously derived model for the cathode heating was applied to some specific gases and electrode materials, and (2) experimental work in which various diagnostics was applied to the cathode. The specific diagnostics used were observation of the cathode tip during arcing using a Laser Strobe Video system in conjunction with a tele-microscope, a monochromator with an optical multichannel analyzer for the determination of the cathode temperature distribution, and various ex situ materials analysis methods. The emphasis of our effort was shifted to the cathode materials analysis because a parallel project was in place during the second half of 1993 with a visiting scientist pursuing arc electrode materials studies. As a consequence, the diagnostic investigations of the arc in front of the cathode had to be postponed to the first half of 1994, and we are presently preparing these measurements. The results of last year's study showed some unexpected effects influencing the cathode erosion behavior, such as increased erosion away from the cathode tip, and our understanding of these effects should improve our ability to control cathode erosion. The arc jet anode attachment studies concentrated on diagnostics of the instabilities in subsonic anode attachment arc jet thrusters, and were supplemental measurements to work which was performed by one of the authors who spent the summer as an intern at NASA Lewis Research Center. A summary of the results obtained during the internship are included because they formed an integral part of the study. Two tasks for 1994, the diagnostics of the anode closure phenomenon, and the use of arc jet thrusters for the deposition of c-BN, are being prepared

Avalanche of Bifurcations and Hysteresis in a Model of Cellular Differentiation

Cellular differentiation in a developping organism is studied via a discrete bistable reaction-diffusion model. A system of undifferentiated cells is allowed to receive an inductive signal emenating from its environment. Depending on the form of the nonlinear reaction kinetics, this signal can trigger a series of bifurcations in the system. Differentiation starts at the surface where the signal is received, and cells change type up to a given distance, or under other conditions, the differentiation process propagates through the whole domain. When the signal diminishes hysteresis is observed

Experimental measurements of plasma properties for Miller SG-100 torch with Mach I setting

In this work measurements of plasma properties, including the fields of temperature, velocity and plasma composition have been completed for the Miller SG-100 plasma torch using argon-helium mixtures with the Mach 1 nozzle at 1 atm pressure. A computer-controlled system combining both spectroscopic and enthalpy probe diagnostics has been developed to allow temperature measurements covering a range from 2000--16000K which includes the plasma flame region which is of interest. The experimental results expose the dominant effects in different spatial areas of argon-helium plasma jets. In the center near the nozzle exit the temperatures exceed 10,000K, and strong diffusion exists due to the steep radial gradients of temperature and particle number densities. In the jet tail region where the temperatures are well below 10,000K and decay in axial and radial direction, the dominant effects in this area are strong cold gas entrainment associated with turbulence. Substantial discrepancies between temperatures evaluated from spectroscopic and enthalpy probe data are particularly severe in the jet fringes indicating that strong deviations from LTE may exist in the jet fringes. In addition, entrainment of the cold surrounding gas into the plasma jet causes severe discrepancies between spectrometric and enthalpy probe data. The validity of the two diagnostic methods will be discussed. The temperature profiles in argon-helium plasma jets are flatter and wider, and the velocities are higher than in a pure argon plasma jet. These features of argon-helium plasma jets may be beneficial for obtaining better performance in the plasma spraying process. 26 refs., 28 figs., 2 tabs

Monitoring Cognitive and Emotional Processes Through Pupil and Cardiac Response During Dynamic Versus Logical Task

The paper deals with the links between physiological measurements and cognitive and emotional functioning. As long as the operator is a key agent in charge of complex systems, the definition of metrics able to predict his performance is a great challenge. The measurement of the physiological state is a very promising way but a very acute comprehension is required; in particular few studies compare autonomous nervous system reactivity according to specific cognitive processes during task performance and task related psychological stress is often ignored. We compared physiological parameters recorded on 24 healthy subjects facing two neuropsychological tasks: a dynamic task that require problem solving in a world that continually evolves over time and a logical task representative of cognitive processes performed by operators facing everyday problem solving. Results showed that the mean pupil diameter change was higher during the dynamic task; conversely, the heart rate was more elevated during the logical task. Finally, the systolic blood pressure seemed to be strongly sensitive to psychological stress. A better taking into account of the precise influence of a given cognitive activity and both workload and related task-induced psychological stress during task performance is a promising way to better monitor operators in complex working situations to detect mental overload or pejorative stress factor of error