5,276 research outputs found
Dynamic parameters of structures extracted from ambient vibration measurements: an aid for the seismic vulnerability assessment of existing buildings in moderate seismic hazard regions
During the past two decades, the use of ambient vibrations for modal analysis
of structures has increased as compared to the traditional techniques (forced
vibrations). The Frequency Domain Decomposition method is nowadays widely used
in modal analysis because of its accuracy and simplicity. In this paper, we
first present the physical meaning of the FDD method to estimate the modal
parameters. We discuss then the process used for the evaluation of the building
stiffness deduced from the modal shapes. The models considered here are 1D
lumped-mass beams and especially the shear beam. The analytical solution of the
equations of motion makes it possible to simulate the motion due to a weak to
moderate earthquake and then the inter-storey drift knowing only the modal
parameters (modal model). This process is finally applied to a 9-storey
reinforced concrete (RC) dwelling in Grenoble (France). We successfully
compared the building motion for an artificial ground motion deduced from the
model estimated using ambient vibrations and recorded in the building. The
stiffness of each storey and the inter-storey drift were also calculated
Fast Color Space Transformations Using Minimax Approximations
Color space transformations are frequently used in image processing,
graphics, and visualization applications. In many cases, these transformations
are complex nonlinear functions, which prohibits their use in time-critical
applications. In this paper, we present a new approach called Minimax
Approximations for Color-space Transformations (MACT).We demonstrate MACT on
three commonly used color space transformations. Extensive experiments on a
large and diverse image set and comparisons with well-known multidimensional
lookup table interpolation methods show that MACT achieves an excellent balance
among four criteria: ease of implementation, memory usage, accuracy, and
computational speed
On Euclidean Norm Approximations
Euclidean norm calculations arise frequently in scientific and engineering
applications. Several approximations for this norm with differing complexity
and accuracy have been proposed in the literature. Earlier approaches were
based on minimizing the maximum error. Recently, Seol and Cheun proposed an
approximation based on minimizing the average error. In this paper, we first
examine these approximations in detail, show that they fit into a single
mathematical formulation, and compare their average and maximum errors. We then
show that the maximum errors given by Seol and Cheun are significantly
optimistic.Comment: 9 pages, 1 figure, Pattern Recognitio
The Determinants of Private Fixed Investment and the Relationship between Public and Private Capital Accumulation in Turkey
The purpose of this study is to analyse the determinants of private fixed investment spending in Turkey over the period 1970–96, which covers years of both financial repression and financial liberalisation. A reformulated neoclassical investment model and a reformulated flexible accelerator investment model have been tested for the Turkish economy. The results obtained support the accelerator principle and the crowding out hypothesis, that is, public and private sector investments have been found to be substitutes. Furthermore, the hypothesis that the volume of funds is as important as the cost of funds used in financing private fixed investment has been verified. On the other hand, the so-called McKinnon-Shaw hypothesis has not been completely verified because the effect of the medium-term real lending rate on private fixed investment has been found to be negative but statistically insignificant. Finally, the financial and liberalisation programmes that have been implemented since 1983 have not yet shown any noticeable positive effects on private investment.
Optical modeling of organic electronic devices
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Physics, 2008.Includes bibliographical references (p. 51-53).Organic materials, with their superior photoluminescence and absorbance properties have revolutionized the technologies for displays and solar energy conversion. Due to the large transition dipoles, the localization of excited states or excitons in organic materials necessitates optical models that extend beyond classical far field methods. In this thesis we propose an extended near field calculation method using dyadic Green's functions and demonstrate the applications of both our extended model and traditional far field models for different types of devices such as surface plasmon detectors, cavity organic light emitting devices and organic photovoltaics with external antennas.by Kemal Celebi.S.M
Approximate Lesion Localization in Dermoscopy Images
Background: Dermoscopy is one of the major imaging modalities used in the
diagnosis of melanoma and other pigmented skin lesions. Due to the difficulty
and subjectivity of human interpretation, automated analysis of dermoscopy
images has become an important research area. Border detection is often the
first step in this analysis. Methods: In this article, we present an
approximate lesion localization method that serves as a preprocessing step for
detecting borders in dermoscopy images. In this method, first the black frame
around the image is removed using an iterative algorithm. The approximate
location of the lesion is then determined using an ensemble of thresholding
algorithms. Results: The method is tested on a set of 428 dermoscopy images.
The localization error is quantified by a metric that uses dermatologist
determined borders as the ground truth. Conclusion: The results demonstrate
that the method presented here achieves both fast and accurate localization of
lesions in dermoscopy images
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