2,325 research outputs found
Experimental investigations of the effects of cutting angle on chattering of a flexible manipulator
When a machine tool is mounted at the tip of a robotic manipulator, the manipulator becomes more flexible (the natural frequencies are lowered). Moreover, for a given flexible manipulator, its compliance will be different depending on feedback gains, configurations, and direction of interest. Here, the compliance of a manipulator is derived analytically, and its magnitude is represented as a compliance ellipsoid. Then, using a two-link flexible manipulator with an abrasive cut off saw, the experimental investigation shows that the chattering varies with the saw cutting angle due to different compliance. The main work is devoted to finding a desirable cutting angle which reduces the chattering
Tradeoffs in manipulator structure and control. Part 1: Summary
The study of various aspects of manipulator design and control is summarized, focusing on the interaction of the structure's flexible dynamics and the dynamics of the joint control system, including specific information on modeling and design, modal analysis and control, and the flexible manipulator analysis computer program, FMAP
Experimental investigation of the fundamental modes of a collisionless plasma Final report, 10 Mar. 1964 - 31 Oct. 1967
Propagation of electron cyclotron waves and effects of low frequency noise in collisionless plasm
Influence of a temperature-dependent shear viscosity on the azimuthal asymmetries of transverse momentum spectra in ultrarelativistic heavy-ion collisions
We study the influence of a temperature-dependent shear viscosity over
entropy density ratio , different shear relaxation times , as
well as different initial conditions on the transverse momentum spectra of
charged hadrons and identified particles. We investigate the azimuthal flow
asymmetries as a function of both collision energy and centrality. The elliptic
flow coefficient turns out to be dominated by the hadronic viscosity at RHIC
energies. Only at higher collision energies the impact of the viscosity in the
QGP phase is visible in the flow asymmetries. Nevertheless, the shear viscosity
near the QCD transition region has the largest impact on the collective flow of
the system. We also find that the centrality dependence of the elliptic flow is
sensitive to the temperature dependence of .Comment: 13 pages, 20 figure
Counting Hamilton cycles in sparse random directed graphs
Let D(n,p) be the random directed graph on n vertices where each of the
n(n-1) possible arcs is present independently with probability p. A celebrated
result of Frieze shows that if then D(n,p) typically
has a directed Hamilton cycle, and this is best possible. In this paper, we
obtain a strengthening of this result, showing that under the same condition,
the number of directed Hamilton cycles in D(n,p) is typically
. We also prove a hitting-time version of this statement,
showing that in the random directed graph process, as soon as every vertex has
in-/out-degrees at least 1, there are typically
directed Hamilton cycles
Collective Bargaining, Teachers and Job Satisfaction
vii, 105 leaves. Advisor: Dr. Charles Rowley.The problem. The study determined what differences
existed between the levels of job satisfaction registered by teachers from schools with certified bargaining units and the levels of job satisfaction registered by teachers from schools without certified bargaining units.
Procedures. The Minnesota Satisfaction Questionnaire, a measure of satisfaction with twenty..,.one different aspects of the work environment, was administered to teachers from
selected Iowa public schools with certified bargaining units and without certified bargaining units. Means were calculated for each job satisfaction scale and the Hotelling's T2, a
multivariate analysis, was conducted. An additional analysis of the data was conducted using the nonparametric chi-square.
Findings. No significant differences existed between the levels of job satisfaction of teachers from schools with certified bargaining units and the levels of job satisfaction of teachers from schools without certified bargaining units.
Conclusions. A review of the literature indicated
varied and complex reasons existed for increased teacher militancy and organization. Teacher dissatisfaction was found to be one of the major factors in increased bargaining activity. However, the findings of the study indicated that teachers from schools with certified bargaining units are no more dissatisfied with twenty-one aspects of their jobs than teachers from schools without certified bargaining units.
Recommendations. The needs of individual staff members
are important. Boards of education and school administrators should create an environment which places an emphasis on the positive contributions of the collective bargaining process that seek to satisfy the needs of individual staff members.
Studies of the leadership styles of administrators and boards of education should be conducted to determine whether or not the type of leadership influenced the job satisfaction levels among the teachers in the study. Replications of this study
in states other than Iowa should be conducted to determine whether teachers who have been involved in the collective bargaining process for shorter or greater periods of time differ significantly in their job satisfaction levels. Similar studies should be conducted examining factors such as age, sex, experience, and training to determine if such demographic data influence teachers' job satisfaction levels
Structure of Supergiant Shells in the Large Magellanic Cloud
Nine supergiant shells (SGSs) have been identified in the Large Magellanic
Cloud (LMC) based on H-alpha images, and twenty-three SGSs have been reported
based on HI 21-cm line observations, but these sets do not always identify the
same structures. We have examined the physical structure of the optically
identified SGSs using HI channel maps and P-V diagrams to analyze the gas
kinematics. There is good evidence for seven of the nine optically identified
SGSs to be true shells. Of these seven H-alpha SGSs, four are the ionized inner
walls of HI SGSs, while three are an ionized portion of a larger and more
complex HI structure. All of the H-alpha SGSs are identified as such because
they have OB associations along the periphery or in the center, with younger OB
associations more often found along the periphery. After roughly 12 Myrs, if no
new OB associations have been formed a SGS will cease to be identifiable at
visible wavelengths. Thus, the presence and location of ionizing sources is the
main distinction between shells seen only in HI and those also seen in H-alpha.
Based on our analysis, H-alpha observations alone cannot unambiguously identify
SGSs, especially in distant galaxies.Comment: 26 pages, 16 figures, accepted for publication in the Astrophysical
Journal Supplemen
Characterizing Strain Accumulation, Residual Stress, and Microstructure of Additive Manufactured Materials
Additive Manufacturing (AM) is a rapidly evolving fabrication technology beneficial for its cost-saving potential to produce complex, low-volume shapes. However, AM materials are currently limited to nonstructural applications due to variability in their structural integrity, particularly their fatigue lives. IN718, Ti64, and Al10MgSi specimens manufactured by Direct Metal Laser Sintering (DMLS) were characterized based on variation of post-processing techniques and build direction. To understand the impact of each variable, surface roughness, hardness, residual stresses, microstructure, and strain accumulation in response to Low Cycle Fatigue (LCF) were studied. The use of Electron Backscatter Diffraction (EBSD) provided grain orientation and grain size distributions in each material. This data also provided a grain boundary overlay to be used in conjunction with in-situ Digital Image Correlation (DIC) during LCF to analyze strain distribution with respect to grain characteristics. This work provides experimental background data to be used for computational modeling of the structural integrity of AM materials in order to establish relationships between microstructure and fatigue. The ultimate goal is to understand the influence of material type, post-processing, and build direction variables in AM processes so these materials can be further explored for structural applications
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