7,041 research outputs found
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Dynamical systems on networks
Get PDF"We obtain results for two distinct dynamical models: the Kuramoto model, a general model for coupled oscillator systems, and a model for opinion formation in social networks. Our main focus is on understanding the fixed points of these systems and their stability. For many models the stability of such fixed points can be studied with a Laplacian matrix. We give a formula for the inertia of these matrices, characterizing the real parts of the spectrum, by relating them to another matrix depending on the network topology. We then study the Kuramoto model, and in particular, the phenomena of synchronization, when all oscillators rotate at a common frequency, which corresponds to a fixed point. This phenomenon is well-known to depend on the natural frequencies of the oscillators and, more specifically, that the chance of synchronization increases if the natural frequencies are more similar. We then give upper and lower bounds for the volume of the set such frequencies in frequency space. Our bounds can be formulated in terms of sums over spanning trees which we further use to deduce that the volume is intimately related to the number of spanning trees for dense networks. We also characterize the structure of fixed points of the Kuramoto model by showing that every fixed point corresponds to a lattice point in a certain set which records how the phase-angles wrap around cycles in the network. As a consequence, under mild conditions, we derive the rate of growth of the number of fixed points as we consider increasingly large graphs with fixed topology. We also consider a model for opinion formation in social networks. More specifically, we characterize the global minima of an energy functional, intuitively the ``most stable"" configurations, when the network is ``balanced"" as well as show that the number of stable configurations can increase as we increase the strengths of the relationships in the network. Finally, we describe an algorithm for generating certain random networks. These networks are generalizations of Erd\H{o}s-R\'{e}nyi graphs with correlations between pairs of edges depending on the particular pattern they create. We then use this algorithm to study the effect on fixed points of network properties and therefore the dynamics of the Kuramoto model."Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2020-05-01The student, Timothy Ferguson, accepted the attached license on 2018-04-11 at 15:36.The student, Timothy Ferguson, submitted this Dissertation for approval on 2018-04-11 at 15:43.This Dissertation was approved for publication on 2018-04-13 at 13:16.DSpace SAF Submission Ingestion Package generated from Vireo submission #12195 on 2018-08-31 at 17:18:27Made available in DSpace on 2018-09-04T20:34:02Z (GMT). No. of bitstreams: 3
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Previous issue date: 2018-04-13Embargo set by: Seth Robbins for item 107236
Lift date: 2020-09-04T20:34:13Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 107236
Lift date: 2020-09-04T20:37:00Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 107236
Lift date: 2020-09-04T20:42:08Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemU of I Only Restriction Lifted for Item 107236 on 2020-09-05T09:15:29Z
Detecting damaged reinforcement bars in concrete structures using guided waves
No full textMany engineering structures must be inspected or monitored throughout their serviceable life to ensure their safe operation. In the case of reinforced concrete structures, the most common cause of premature failure is corrosion of the steel reinforcement bars that must be pre-empted. Modal based techniques are popular, since they can potentially detect damage using sensors placed remotely from the damage site. However, changes in modal parameters due to damage can be masked by their sensitivity to environmental factors and changes to the boundary conditions that are unrelated to damage. In this respect, wave based techniques provide a potential alternative. In this paper, wave propagation is modelled in a damaged steel reinforced concrete beam. The damaged section is modelled in conventional finite elements and this is coupled to wave finite element models (WFE) of the undamaged sections on either side. This hybrid modelling approach facilitates a wave based analysis of a one dimensional structure with potentially geometrically complex damage. A numerical case study is presented for a locally damaged beam represented by a loss of thickness of one reinforcement bar. It is shown that some wave modes, that feature deformation of the cross section, exhibit a strong reflection close to their cut-on frequency. This is due to the difference in cut-on frequency between the damaged and undamaged sections. A damage detection method is outlined in which the amplitudes of incident and reflected waves of low wave number are compared. No a priori knowledge of the dispersion curves is necessary. In numerical simulations, a reduction in the ratio of the reflected to incident wave amplitudes is seen in the vicinity of cut-on frequencies
Guided wave inspection of bars in reinforced-concrete beams using surface-mounted vibration sensors
No full textSteel reinforcement bars (rebars) in concrete structures are inaccessible and not conducive to many inspection methods. This paper proposes a non-invasive technique based on guided waves for detecting localised abnormalities in rebars embedded in concrete beams. The technique is predicated on previously published observations that guided waves are strongly reflected by discontinuities at the frequency at which they begin to propagate, i.e., at cut-on. The reflection coefficient at cut-on is estimated using a simple wave decomposition in which a near-zero wavenumber value is assumed. A simulated study is first carried out to evaluate the technique on a concrete beam featuring four rebars. The wave finite element approach is adopted to model two uniform beams which are coupled via a short, damaged section modelled in conventional finite element analysis. Estimated reflection coefficients arising from the discontinuity are close to the true values at cut-on and independent of frequency elsewhere, so that no prior knowledge of cut-on frequencies is required. Three steel-reinforced concrete beams were fabricated—one uniform and two with localised rebar damage—and reflection coefficients were estimated from measured transfer functions. As predicted, abrupt deviations in the reflection coefficient occurred at cut-on frequencies for both damaged beams
Application of the wave finite element method to reinforced concrete structures with damage
No full textVibration based methods are commonly deployed to detect structural damage using sensors placed remotely from potential damage sites. Whilst many such techniques are modal based there are advantages to adopting a wave approach, in which case it is essential to characterise wave propagation in the structure. The Wave Finite Element method (WFE) is an efficient approach to predicting the response of a composite waveguide using a conventional FE model of a just a short segment. The method has previously been applied to different structures such as laminated plates, thinwalled structures and fluid-filled pipes. In this paper, the WFE method is applied to a steel reinforced concrete beam. Dispersion curves and wave mode shapes are first presented from free wave solutions, and these are found to be insensitive to loss of thickness in a single reinforcing bar. A reinforced beam with localised damage is then considered by coupling an FE model of a short damaged segment into the WFE model of the undamaged beam. The fundamental bending, torsion and axial waves are unaffected by the damage but some higher order waves of the cross section are significantly reflected close to their cut-on frequencies. The potential of this approach for detecting corrosion and delamination in reinforced concrete beams will be investigated in future work
Application of the wave finite element method to reinforced concrete structures with damage
No full textVibration based methods are commonly deployed to detect structural damage using sensors placed remotely from potential damage sites. Whilst many such techniques are modal based there are advantages to adopting a wave approach, in which case it is essential to characterise wave propagation in the structure. The Wave Finite Element method (WFE) is an efficient approach to predicting the response of a composite waveguide using a conventional FE model of a just a short segment. The method has previously been applied to different structures such as laminated plates, thinwalled structures and fluid-filled pipes. In this paper, the WFE method is applied to a steel reinforced concrete beam. Dispersion curves and wave mode shapes are first presented from free wave solutions, and these are found to be insensitive to loss of thickness in a single reinforcing bar. A reinforced beam with localised damage is then considered by coupling an FE model of a short damaged segment into the WFE model of the undamaged beam. The fundamental bending, torsion and axial waves are unaffected by the damage but some higher order waves of the cross section are significantly reflected close to their cut-on frequencies. The potential of this approach for detecting corrosion and delamination in reinforced concrete beams will be investigated in future work
Wave propagation in reinforced and prestressed concrete structures with damage
No full textCorrosion of the steel reinforcement bars in reinforced concrete is the most common cause of premature failure that must be pre-empted. In this respect, wave based techniques provide a potential detection approach. In this paper, wave propagation is modelled in a steel reinforced concrete beam with and without prestress. A short section of the beam is modelled in ANSYS. This model is then used in the wave finite element (WFE) framework, which assumes spatial periodicity along the waveguide, to model a beam of infinite extent. Corrosion of the reinforcement bars is represented by a local loss of thickness. Numerical case studies are presented to investigate the effects of various configurations and the severity of damage on the dispersion curves of the propagating waves. Scattering matrices are also calculated for the damage site, by coupling damaged and undamaged sections of the waveguide. Wave modes are subsequently identified for which the reflection coefficients are potentially sufficiently large to observe and use for damage identification
Money piece by Timothy P. Agnew, chief executive officer of the Finance Author
No full textMoney piece by Timothy P. Agnew, chief executive officer of the Finance Authority of Maine, about the increased availability of credit for Maine\u27s small businesses
Wave propagation and scattering in reinforced concrete beams
Get PDFSteel reinforcement bars (rebars) are vital to the strength of reinforced concrete (RC) structures, but can become damaged due to corrosion. Such damage is generally invisible and non-destructive testing methods are needed to assess their integrity. Guided wave methods are popular because they are capable of detecting damage using sensors placed remotely from the damage site, which is often unknown. This paper predicts free wave propagation in RC beams from which the concept of a guided wave based damage detection method emerges. The wave solutions are obtained using the wave finite element framework where a short section of a beam’s cross section is modeled in conventional finite element (FE) and periodic boundary conditions are subsequently applied. Reinforcement elements are used in the FE model of the cross section as a neat and efficient means of coupling the concrete to the rebars and imposing prestress. The results show that prestress, important for static behavior, has a negligible effect on wave dispersion. A RC beam with a damaged section is modeled by coupling three waveguides, the center waveguide being identical to the outer ones except for a thickness loss in one rebar. Only small differences in cut-on frequencies are observed between the damaged and undamaged sections. However, these small differences give rise to strong reflection of some waves at frequencies close to cut-on. Below cut-on, most incident power is transmitted but experiences wave mode conversion, whereas above cut-on most power is transmitted to the same wave type. These observations form the basis for ongoing work to develop a damage detection technique premised on wave reflection near cut-on
Timothy Meyer serves as a contributing author for UN report
No full textAssistant Professor Timothy Meyer served as a contributing author for the United Nations Industrial Development Organization\u27s report titled Networks for Prosperity: Connecting Development Knowledge Beyond 2015. The document, which was released during November, analyzes the nexus between the global connectedness of a country and its economic success, sustainability and government effectiveness. Meyer was one of only approximately 20 academic and practical experts from around the world selected to serve as a contributor after a global call for proposals.
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