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 $\eta/s$, different shear relaxation times $\tau_\pi$, 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 $\eta/s$.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 $p\ge(\log n+\omega(1))/n$ 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 $n!(p(1+o(1)))^{n}$. 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 $n!(\log n/n(1+o(1)))^{n}$ 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