1,666 research outputs found
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
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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 OC and OC 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 OC system. The relation between the obtained potentials and
those reported for the symmetrical OO and CC
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 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
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