Vaughn College of Aeronautics and Technology

About: Vaughn College of Aeronautics and Technology is a education organization based out in New York, New York, United States. It is known for research contribution in the topics: Gravitational microlensing & Planetary system. The organization has 727 authors who have published 708 publications receiving 14082 citations. The organization is also known as: College of Aeronautics.

Study of a magnetorheological brake under compression-shear mode

Abstract: A magnetorheological (MR) brake under compression-shear mode is designed, simulated and experimentally investigated in this paper. A MR brake under compression-shear mode was first designed considering compression enhanced shear yield stress of MR fluid. Then, the operating principle of the MR brake was illustrated and mathematical torque expressions, operating under compression-shear mode assuming Herschel–Bulkley model, was further established. Moreover, simulation analysis of the designed magnetic circuit was performed as well. An experimental prototype was fabricated and tested to evaluate the transmission performance of MR brake. The results showed that the large torque could be produced at high applied currents, high compressive stress, large compressive strain and small initial gap distances. The rotational speed and compressive speed had little effect on the torque. The characteristic rising time of the torque was greatly affected by the rotational speed, the compressive strain, and compressive speed. However, the current had little effect on the rising time. The time constant would became shorter when both the rotational speed and the compressive speed were faster. Through analyzing the compression of particle chains in MR fluids directly, it was found that the diameter and the length of the particles chains brought a strong influence on the essential property of MR fluids under compression. Thus, the compressive stress or compressive strain and the initial gap distance also played an important role in enhancing the torque. The results also showed that the proposed MR brake could generate a maximum torque of 241 Nm, about 17.9 times the magnitude of braking torque without compression, and achieve a high torque density of 125.6 kN m–2 and a time constant of 58 ms. This study provides a better understanding of MR brake under compression-shear mode and the implications for many high-power applications.

The exceptional abandonment of metal tools by North American hunter-gatherers, 3000 B.P.

Abstract: Most prehistoric societies that experimented with copper as a tool raw material eventually abandoned stone as their primary medium for tool making. However, after thousands of years of experimentation with this metal, North American hunter-gatherers abandoned it and returned to the exclusive use of stone. Why? We experimentally confirmed that replica copper tools are inferior to stone ones when each is sourced in the same manner as their archaeological counterparts and subjected to identical tasks. Why, then, did copper consistently lead to more advanced metallurgy in most other areas of the world? We suggest that it was the unusual level of purity in the North American copper sourced by North American groups, and that naturally occurring alloys yielded sufficiently superior tools to encourage entry into the copper-bronze-iron continuum of tool manufacture in other parts of the world.

Reaction-Broadening in a Hydrogen-Oxygen Diffusion Flame

Abstract: The present paper is a continuation of the study of diffusion flames in a hydrogen-oxygen mixture which began with an investigation of equilibrium-broadening by the writer (1968). In the present model the hydrogen dissociation reaction is assumed to be so slow that it can be neglected. The effect of the remaining reaction rates on flame structure is then investigated by the method of matched asymptotic expansions, which provides information about the orders of magnitude of the various species' concentrations, and identifies simplified sets of equations which govern behaviour in various regions of the flame. The general forms of the solutions are established; attention is confined to analytical questions.

Energy transfer through a dissociated diatomic gas in Couette flow

Abstract: The transfer of energy through a dissociated diatomic gas in Couette flow is considered, taking oxygen as a numerical example. The two extremes of chemical equilibrium flow and chemically frozen flow are dealt with in detail, and it is shown that the surface reaction rate is of prime importance in the latter case. The chemical rate equations in the gas phase are used to estimate the probable chemical state of the gas mixture, this being deduced from the ratio of a characteristic chemical reaction time to a characteristic time for atom diffusion across the layer. The influence of the surface reaction appears to spread outwards through the flow from the wall as gas-phase chemical reaction times decrease. For practical values of the surface reaction rate on a metallic wall, the energy transfer rate may be significantly lower in chemically frozen flow than in chemical equilibrium flow under otherwise similar circumstances.Similar phenomena to those discussed will arise in the more complicated case of boundary layer flows, so that a treatment of the simpler type of shear layer represented by Couette flow may be of some value in assessing the relative importance of the various parameters.