1,663 research outputs found
Speech Analysis
Contains research objectives and reports on one research project.National Science Foundatio
Influence of Different Material Models on the Result of Numerical High Speed Cutting Simulations
Extreme conditions for the workpiece and the tool can occur in high speed cutting processes. Temperatures above 1000 °C at very high strains over 3 and strain rates near 105 1/s are not unusual. In the first part of this paper an overview about the well known and new developed testing methods for these extreme conditions is given. For numerical simulations it is necessary to formulate closed material models which include strain, strain rate, and the temperature. In the second part some well known material models are presented and compared. Furthermore, advantages and disadvantages are named. The flow stress behaviour of two types of steel (1.1191, 1.2311) as a function of strain rate and temperature is presented. A Johnson-Cook and a Zerilli-Armstrong model is used for the comparative numerical simulations of an orthogonal cutting process. To indicate the process of chip segmentation, a damage model is often used. The influence of various damage models with different damage parameters and failure modes is shown. The calculated cutting forces and the shape of the chips are compared with results determined at a quickstop cutting device with integrated force measurement. Additionally, the calculated chip formation is compared with the measured shape by means of highspeed photography. The temperatures, forces, and chip shape for both used models are presented and the influence of different material models are evaluated and named
The COMPLETE Survey of Outflows in Perseus
We present a study on the impact of molecular outflows in the Perseus
molecular cloud complex using the COMPLETE survey large-scale 12CO(1-0) and
13CO(1-0) maps. We used three-dimensional isosurface models generated in
RA-DEC-Velocity space to visualize the maps. This rendering of the molecular
line data allowed for a rapid and efficient way to search for molecular
outflows over a large (~ 16 sq. deg.) area. Our outflow-searching technique
detected previously known molecular outflows as well as new candidate outflows.
Most of these new outflow-related high-velocity features lie in regions that
have been poorly studied before. These new outflow candidates more than double
the amount of outflow mass, momentum, and kinetic energy in the Perseus cloud
complex. Our results indicate that outflows have significant impact on the
environment immediately surrounding localized regions of active star formation,
but lack the energy needed to feed the observed turbulence in the entire
Perseus complex. This implies that other energy sources, in addition to
protostellar outflows, are responsible for turbulence on a global cloud scale
in Perseus. We studied the impact of outflows in six regions with active star
formation within Perseus of sizes in the range of 1 to 4 pc. We find that
outflows have enough power to maintain the turbulence in these regions and
enough momentum to disperse and unbind some mass from them. We found no
correlation between outflow strength and star formation efficiency for the six
different regions we studied, contrary to results of recent numerical
simulations. The low fraction of gas that potentially could be ejected due to
outflows suggests that additional mechanisms other than cloud dispersal by
outflows are needed to explain low star formation efficiencies in clusters.Comment: Published in The Astrophysical Journa
Linguistics
Contains research objectives and reports on one research project.National Institutes of Health (Grant 1 P01 MH-13390-02
Speech Communication
Contains reports on four research projects.National Science FoundationUnited States Air Force, Air Force Cambridge Research Center, Air Research and Development Command (Contract AF19(604)-2061
The generalized holographic stereogram
Thesis (M.S.V.S.)--Massachusetts Institute of Technology, Dept. of Architecture, 1991.Includes bibliographical references (leaves 123-124).by Michael W. Halle.M.S.V.S
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