Vibration-Based Damage Detection in Wind Turbine Blades using Phase-Based Motion Estimation and Motion Magnification

Vibration-based Structural Health Monitoring (SHM) techniques are among the most common approaches for structural damage identification. The presence of damage in structures may be identified by monitoring the changes in dynamic behavior subject to external loading, and is typically performed by using experimental modal analysis (EMA) or operational modal analysis (OMA). These tools for SHM normally require a limited number of physically attached transducers (e.g. accelerometers) in order to record the response of the structure for further analysis. Signal conditioners, wires, wireless receivers and a data acquisition system (DAQ) are also typical components of traditional sensing systems used in vibration-based SHM. However, instrumentation of lightweight structures with contact sensors such as accelerometers may induce mass-loading effects, and for large-scale structures, the instrumentation is labor intensive and time consuming. Achieving high spatial measurement resolution for a large-scale structure is not always feasible while working with traditional contact sensors, and there is also the potential for a lack of reliability associated with fixed contact sensors in outliving the life-span of the host structure. Among the state-of-the-art non-contact measurements, digital video cameras are able to rapidly collect high-density spatial information from structures remotely. In this paper, the subtle motions from recorded video (i.e. a sequence of images) are extracted by means of Phase-based Motion Estimation (PME) and the extracted information is used to conduct damage identification on a 2.3-meter long Skystream wind turbine blade (WTB). The PME and phased-based motion magnification approach estimates the structural motion from the captured sequence of images for both a baseline and damaged test cases on a wind turbine blade

The Future of Weak Ties

“The Strength of Weak Ties” (Granovetter 1973) arguably contains the most influential sociological theory of networks. Granovetter’s subtle, nuanced theory has spawned countless follow-on ideas, many of which are immortalized in the 35,000 manuscripts that cite the original work. Among these are notable theories in their own right, such as Ron Burt’s structural holes theory (Burt 1992), which itself has generated a sizable body of knowledge about the social structure of competition

Desire for Power and Change in J.R.R. Tolkien’s Lord of the Rings: Return of the King.

This extended essay is an analysis of theme power and the desire for power of the characters in J.R.R. Tolkien’s Lord of the Rings: Return of the King and consists of an examination of question: ‘How does Tolkien give the illustration of the human desire for power symbolized by the ring and demonstrates the alteration of the characters when they wear the ring in Lord of the Rings: Return of the King?’; with references to the final novel of the trilogy and when necessary some secondary sources. Some quotations from the published literary is used to clarify the points given with the examples from the piece of literature. This essay analyses the topic: ‘Desire for Power and Change in J.R.R. Tolkien’s Lord of the Rings-Return of the King.’ by giving the change of some particular characters: Frodo, Sauron, Gollum and Denethor. Each of the analysis of the change of the characters is focusing on a different aspect of the examination. With the first character, Denethor, the desire for power and letting it go is given and contrary to Denethor, Aragorn is given to show the contraction between good and evil. Second character, Sauron, is given to show the control of power and what power is capable of. Gollum, the third character, shows the changes of a character under the desire of power and Frodo shows the mental change and the change in aim

Sen, mutluluğun resmini yapabilir misin Abidin?

Taha Toros Arşivi, Dosya No: 178-Abidin Dino. Not: Gazetenin "Düşünenlerin Düşüncesi" köşesinde yayımlanmıştır

IT Assets, Organizational Capabilities, and Firm Performance: How Resource Allocations and Organizational Differences Explain Performance Variation

Despite evidence of a positive relationship between information technology (IT) investments and firm performance, results still vary across firms and performance measures. We explore two organizational explanations for this variation: differences in firms’ IT investment allocations and their IT capabilities. We develop a theoretical model of IT resources, defined as the combination of specific IT assets and organizational IT capabilities. We argue that investments into different IT assets are guided by firms’ strategies (e.g., cost leadership or innovation) and deliver value along performance dimensions consistent with their strategic purpose. We hypothesize that firms derive additional value per IT dollar through a mutually reinforcing system of organizational IT capabilities built on complementary practices and competencies. Empirically, we test the impact of IT assets, IT capabilities, and their combination on four dimensions of firm performance: market valuation, profitability, cost, and innovation. Our results—based on data on IT investment allocations and IT capabilities in 147 U.S. firms from 1999 to 2002—demonstrate that IT investment allocations and organizational IT capabilities drive differences in firm performance. Firms’ total IT investment is not associated with performance, but investments in specific IT assets explain performance differences along dimensions consistent with their strategic purpose. In addition, a system of organizational IT capabilities strengthens the performance effects of IT assets and broadens their impact beyond their intended purpose. The results help explain variance in returns to IT capital across firms and expand our understanding of alignment between IT and organizations. We illustrate our findings with examples from a case study of 7-Eleven JapanNYU, Stern School of Business, IOMS department, Center for Digital Economy Researc

Networks, Information & Social Capital

This paper is based on a draft formerly titled “Network Structure & Information Advantage.”This paper investigates how information flows enable social networks to constitute social capital. By analyzing the information content encoded in email communication in an executive recruiting firm, we examine the long held but empirically untested assumption that diverse networks drive economic performance by providing access to novel information. We show that diverse networks provide diverse, novel information, and that access to novel information predicts productivity and performance. But whether diverse networks deliver novel information depends on a tradeoff between network diversity and communication channel bandwidth: as networks become diverse, channel bandwidth contracts. As network diversity and channel bandwidth both enable access to more novel information, diverse networks provide more novel information (a) when the topic space is large, (b) when topics are distributed non-uniformly across nodes and (c) when information in the network changes frequently. Diverse networks are not just pipes into diverse knowledge pools, but also inspire non-redundant communication even when the knowledge endowments of contacts are homogenous. Consistent with theories of cognitive capacity, bounded rationality, and information overload, there are diminishing marginal productivity returns to novel information. Network diversity also contributes to performance when controlling for the performance effects of novel information, suggesting additional non-information based benefits to structural diversity. These analyses unpack the mechanisms that enable information advantages in networks and serve as a 'proof-of-concept' for using email content to analyze relationships between information, networks and social capital in organizations.The National Science Foundation, Cisco Systems Inc., France Telecom and the MIT Center for Digital Business

Superluminous supernovae: No threat from Eta Carinae

Recently Supernova 2006gy was noted as the most luminous ever recorded, with a total radiated energy of ~10^44 Joules. It was proposed that the progenitor may have been a massive evolved star similar to eta Carinae, which resides in our own galaxy at a distance of about 2.3 kpc. eta Carinae appears ready to detonate. Although it is too distant to pose a serious threat as a normal supernova, and given its rotation axis is unlikely to produce a Gamma-Ray Burst oriented toward the Earth, eta Carinae is about 30,000 times nearer than 2006gy, and we re-evaluate it as a potential superluminous supernova. We find that given the large ratio of emission in the optical to the X-ray, atmospheric effects are negligible. Ionization of the atmosphere and concomitant ozone depletion are unlikely to be important. Any cosmic ray effects should be spread out over ~10^4 y, and similarly unlikely to produce any serious perturbation to the biosphere. We also discuss a new possible effect of supernovae, endocrine disruption induced by blue light near the peak of the optical spectrum. This is a possibility for nearby supernovae at distances too large to be considered "dangerous" for other reasons. However, due to reddening and extinction by the interstellar medium, eta Carinae is unlikely to trigger such effects to any significant degree.Comment: 19 pages, 2 figures; Revised version as accepted for publication in Astrobiolog