Design and use of a fixed-end low-load material testing machine

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2000.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (leaf 25).The purpose of this low-load material testing machine is to provide students an opportunity to perform basic material tests on their own instead of watching a lab technician, thus improving the student's lab experience. The machine proposed is small, low cost, and easy to manufacture, assemble, and operate. Its design is based on a compound flexure mechanism that provides rectilinear motion for uniaxial tension and compression tests. It is actuated by a voice coil and displacement is measured using strain gauges. This thesis outlines some of the basic theory involved in the design and use of this low-load machine. Then it details calibration routines and tension testing procedures. Next, it analyzes results from tension tests. Then it discusses a possible source of error found in the tension tests, a lack of rigidity in the apparatus. Finally, it provides a reasonable solution to the rigidity issue and suggests further testing of the new apparatus before it is available for student use.by Nicoli M. Ames.S.B

Dynamical Renormalization Group Study for a Class of Non-local Interface Equations

We provide a detailed Dynamic Renormalization Group study for a class of stochastic equations that describe non-conserved interface growth mediated by non-local interactions. We consider explicitly both the morphologically stable case, and the less studied case in which pattern formation occurs, for which flat surfaces are linearly unstable to periodic perturbations. We show that the latter leads to non-trivial scaling behavior in an appropriate parameter range when combined with the Kardar-Parisi-Zhang (KPZ) non-linearity, that nevertheless does not correspond to the KPZ universality class. This novel asymptotic behavior is characterized by two scaling laws that fix the critical exponents to dimension-independent values, that agree with previous reports from numerical simulations and experimental systems. We show that the precise form of the linear stabilizing terms does not modify the hydrodynamic behavior of these equations. One of the scaling laws, usually associated with Galilean invariance, is shown to derive from a vertex cancellation that occurs (at least to one loop order) for any choice of linear terms in the equation of motion and is independent on the morphological stability of the surface, hence generalizing this well-known property of the KPZ equation. Moreover, the argument carries over to other systems like the Lai-Das Sarma-Villain equation, in which vertex cancellation is known {\em not to} imply an associated symmetry of the equation.Comment: 34 pages, 9 figures. Journal of Statistical Mechanics: Theory and Experiments (in press

From outsiders to insiders? Strategies and practices of American film distributors in post-war Italy

This article examines the impact of structural changes in the postwar film industry on the activities and effectiveness of the foreign distribution subsidiaries of American firms. As these subsidiaries saw their regular supply of films from their in-house Hollywood studios decline, they sought out alternative sources of product content, often from local markets. Unable to rely on the traditional “ownership” advantages bestowed on them by their parent firms, these subsidiaries increasingly needed to integrate into local networks and forge closer relationships with local producers and exhibitors. Our focus is on Italy, one of the most important film markets for US companies in the 1960s. We collect data on the box office revenues and screen time allocated to every film released into the first-run cinema market and compare the effectiveness of American versus Italian distributors in maximizing the exposure of their most popular films. We explore the attempts by US firms to form partnerships with Italian distributors and producers. Finally, we examine available archival records to reveal the detailed activities of US distribution offices in Italy and their attempts to integrate into local business networks. We conclude that while US subsidiaries did not fully succeed in becoming “insiders” within the Italian film industry in this period, they did actively work toward such an objective

Partner selection in indoor-to-outdoor cooperative networks: an experimental study

In this paper, we develop a partner selection protocol for enhancing the network lifetime in cooperative wireless networks. The case-study is the cooperative relayed transmission from fixed indoor nodes to a common outdoor access point. A stochastic bivariate model for the spatial distribution of the fading parameters that govern the link performance, namely the Rician K-factor and the path-loss, is proposed and validated by means of real channel measurements. The partner selection protocol is based on the real-time estimation of a function of these fading parameters, i.e., the coding gain. To reduce the complexity of the link quality assessment, a Bayesian approach is proposed that uses the site-specific bivariate model as a-priori information for the coding gain estimation. This link quality estimator allows network lifetime gains almost as if all K-factor values were known. Furthermore, it suits IEEE 802.15.4 compliant networks as it efficiently exploits the information acquired from the receiver signal strength indicator. Extensive numerical results highlight the trade-off between complexity, robustness to model mismatches and network lifetime performance. We show for instance that infrequent updates of the site-specific model through K-factor estimation over a subset of links are sufficient to at least double the network lifetime with respect to existing algorithms based on path loss information only.Comment: This work has been submitted to IEEE Journal on Selected Areas in Communications in August 201

Kardar-Parisi-Zhang asymptotics for the two-dimensional noisy Kuramoto-Sivashinsky equation

We study numerically the Kuramoto-Sivashinsky (KS) equation forced by external white noise in two space dimensions, that is a generic model for e.g. surface kinetic roughening in the presence of morphological instabilities. Large scale simulations using a pseudospectral numerical scheme allow us to retrieve Kardar-Parisi-Zhang (KPZ) scaling as the asymptotic state of the system, as in the 1D case. However, this is only the case for sufficiently large values of the coupling and/or system size, so that previous conclusions on non-KPZ asymptotics are demonstrated as finite size effects. Crossover effects are comparatively stronger for the 2D case than for the 1D system.Comment: 5 pages, 3 figures; supplemental material available at journal web page and/or on reques

Analytical approximation for the sphere-sphere Coulomb potential

A simple analytical expression, which closely approximates the Coulomb potential between two uniformly charged spheres, is presented. This expression can be used in the optical potential semiclassical analyses which require that the interaction be analytic on and near the real r-axis.Comment: 4 pages including 3 figures and 1 tabl

Refractive elastic scattering of carbon and oxygen nuclei: The mean field analysis and Airy structures

The experimental data on the $^{16}$O$+^{12}$C and $^{18}$O$+^{12}$C elastic scatterings and their optical model analysis are presented. Detailed and complete elastic angular distributions have been measured at the Strasbourg Vivitron accelerator at several energies covering the energy range between 5 and 10 MeV per nucleon. The elastic scattering angular distributions show the usual diffraction pattern and also, at larger angles, refractive effects in the form of nuclear rainbow and associated Airy structures. The optical model analysis unambiguously shows the evolution of the refractive scattering pattern. The observed structure, namely the Airy minima, can be consistently described by a nucleus-nucleus potential with a deep real part and a weakly absorptive imaginary part. The difference in absorption in the two systems is explained by an increased imaginary (mostly surface) part of the potential in the $^{18}$O$+^{12}$C system. The relation between the obtained potentials and those reported for the symmetrical $^{16}$O$+^{16}$O and $^{12}$C$+^{12}$C systems is drawn.Comment: 10 pages, 9 figures, Phys. rev. C in pres

Faceted anomalous scaling in the epitaxial growth of semiconductor films

We apply the generic dynamical scaling theory (GDST) to the surfaces of CdTe polycrystalline films grown in glass substrates. The analysed data were obtained with a stylus profiler with an estimated resolution lateral resolution of $l_c=0.3 \mu$m. Both real two-point correlation function and power spectrum analyses were done. We found that the GDST applied to the surface power spectra foresees faceted morphology in contrast with the self-affine surface indicated by the local roughness exponent found via the height-height correlation function. This inconsistency is explained in terms of convolution effects resulting from the finite size of the probe tip used to scan the surfaces. High resolution AFM images corroborates the predictions of GDST.Comment: to appear in Europhysics Letter

Walking Quadrupedal Platform

The goal of this project was to continue developing a functioning quadrupedal platform for the WPI robotics department. The quadruped is a forty-pound robot with four independently moving legs built by a previous MQP. This project consists of testing and implementing motion control systems. The primary goal of the project was to ensure that the robot quadrupedal chassis built by a previous MQP could move stably and intelligently so that it can be useful for future projects. Three main motion gaits were studied, a crawl gait, a walking gait, and a turning gait. The project implemented stable motion for the three gaits mentioned. In addition, the team also made significant system design improvements in the structure, electrical circuit, and code