2,273 research outputs found
On the performance of a nonlinear vibration isolator consisting of axially loaded curved beams
No full textA desirable characteristic for nonlinear vibration isolators is a high static stiffness and a low dynamic stiffness. A curved beam is a possible candidate for this role provided that the amplitude of vibration about the static equilibrium position is sufficiently small. However, for large amplitude oscillations, the nonlinear dynamics may have a detrimental effect. This paper considers the force transmissibility of a single degree-of-freedom system where the stiffness element is a curved, axially loaded beam. The transmitted force is calculated by numerical time domain integration of the equations of motion. The exact force-deflection relation for the beam is used for the spring. By comparison, a frequency domain solution is sought using the Harmonic Balance (HB) method in which the system is modelled as a Duffing oscillator. It is shown that the HB and time domain solutions are in close agreement for small amplitudes of excitation and both predict advantageous performance of the nonlinear isolator compared with its equivalent linear counterpart. However, significant discrepancies occur between the two solutions for large excitation since the beam can no longer be approximated by a linear and a cubic stiffness. It is also strongly asymmetric – soft in compression but stiff in extreme extension– which gives rise to an impulse in the transmitted force in each fundamental period. This numerical problem is alleviated by inserting a linear spring in series with the beam isolator with a modest compromise in isolation performance at the excitation frequency
Locating damage in waveguides from the phase of point frequency response measurements
No full textA method for detecting damage in uniform waveguide structures from two or more point frequency response functions (FRFs) is described. Attention is focussed on bending waves in beams although the method can in principle be applied to any waveguide structure. The input FRF is the superposition of directly injected waves and waves reflected from the damage and from other scattering regions in the structure. The phase of this FRF modulates with wavenumber, with the period of modulation in wavenumber space being related to the distances between the excitation point and scattering locations. The phase spectrum of the input FRF is found: the phase is determined, dispersive effects are removed by transforming from the frequency domain to the wavenumber domain, and the inverse Fourier transform from the wavenumber to the space domain found. Peaks in this phase spectrum indicate the distance to the scatterer. Two (or more) input FRFs can be used to determine the location of the scatterer unambiguously. Signal processing issues are discussed. Numerical results for a uniform beam with a breathing crack are given and experimental results for beams with a slot cut into them are presented. The approach lies in the middle ground between low frequency, modal methods and high frequency, ultrasonic methods. It allows one to interrogate a region of a structure rather than the complete structure and there is no requirement for a validated model of the structure in order to locate damage, apart from an estimate of the dispersion relation
‘Much of Sala, and but Little of Russia''A Journey Due North,' Household Words, and the Birth of a Special Correspondent
No full textWhen Dickens sent George Augustus Sala as a special correspondent to Russia just after the end of the Crimean War, he launched him in what was to become his best-known role as a journalist. Comprising twenty-two articles which appeared in weekly instalments from 4 October 1856 to 14 March 1857, Sala's essays are of interest not only for their representation of one of the significant geographical and cultural "others" of the mid-Victorian imagination, but for their distinctive style, which is vibrant and polyglot, eschewing political analysis and statistical information in favour of the flâneur's "gastronomy of the eye" – the vivid metropolitan travel writing so popular with mid-nineteenth-century readers
Evaluating Citebase, an open access Web-based citation-ranked search and impact discovery service
No full textCitebase is a new citation-ranked search and impact discovery service that measures citations of scholarly research papers which are openly accessible on the Web, i.e. papers that are assessable continuously online. Other services, such as ResearchIndex, have emerged in recent years to offer citation indexing of Web research papers. In the first detailed user evaluation of an open access Web citation indexing service, Citebase has been evaluated by nearly 200 users from different backgrounds. The paper details the procedures used in the evaluation, and analyses the results of this study, which took place between June and October 2002. It was found that within the scope of its primary components, the search interface and services available from its rich bibliographic records, Citebase can be used simply and reliably for the purpose intended, and that it compares favourably with other bibliographic services. It is shown tasks can be accomplished efficiently with Citebase regardless of the background of the user. More data need to be collected and the process refined before it is as reliable for measuring citation impact of indexed papers. Better explanations and guidance are required for first-time users. Coverage is seen as a limiting factor, even though Citebase indexes over 200,000 papers from arXiv. Non-physicists were frustrated at the lack of papers from other sciences. The principle of citation searching of open access archives has thus been demonstrated and need not be restricted to current users. Since the evaluation, Citebase has become a featured service of the ArXiv physics eprint archives
Author Talk
No full textUniversity president, Jim Schmotter, introduces Tim O'Brien at the author talk in Ives Auditorium, October 26, 2010.</p
Who Belongs? Immigrants, Refugees, Migrants, and Actions Towards Justice: A Conversation With Tim Wise
No full textTim Wise is an antiracist activist, essayist and author of seven books on racism, inequality and white privilege. He is among the most prominent anti-racist writers and educators in the United States. Over the past 25 years he has engaged audiences in all 50 states, at over 1000 college and high school campuses, at hundreds of professional and academic conferences, and to community groups across the country. While visiting Iowa State University Tim Wise interviewed with us to discuss Who Belongs? by providing a brief historical perspective of immigration, the current political climate, and the role of activism.</p
Investigating the influence of drone flight on the stability of cancer medicines.
No full textMonoclonal Antibodies (mAbs) are being used in the treatment of both malignant and non-malignant diseases and whilst highly effective, certain products have very short expiry times. Clinical deterioration and supply chain disruption can often lead to wastage and there is a need to reduce this by improving efficiency in logistics practices between manufacturing sites and administration locations. This study aimed to investigate the influence of drone flight on the stability of cancer medicines. Clinically expired, premanufactured monoclonal antibodies (mAbs) were investigated, contained inside instrumented Versapaks, and flown in a Skylift (Mugin) V50 vertical take-off and landing drone through seven phases of flight, (take-off, hover, transition, cruise, transition, hover, and landing). Storage specifications (2-8°C) were met, and any vibrations emanating from the drone and transmitted through the packaging during flight were monitored using accelerometers. Vibration occurred largely above 44 Hz which was consistent with rotor speeds during operation and was significantly greater in amplitude during transition than in forward flight or in hover. Bench experiments validated assurance practices, exploring the edge-of-quality failure by applying extremes of rotational vibration to the mAbs. Aggregation and fragmentation represented a loss of quality in the mAbs and would pose a risk to patient safety. No significant difference was identified in the aggregation and fragmentation of all flown mAbs samples, indicating structural integrity. Flown mAbs in their infusion bags had similar particle sizes compared to controls, (Bevacizumab 11.8±0.17 nm vs. 11.6±0.05 nm, Trastuzumab 11.2±0.05 nm vs. 11.3±0.13 nm, Rituximab 11.4±0.27 nm vs. 11.5±0.05 nm) and aggregate content (Bevacizumab 1.25±0.03% vs 1.32±0.02% p = 0.11, Trastuzumab 0.15±0.06% vs. 0.16±0.06% p = 0.75, Rituximab 0.11±0.02% vs. 0.11±0.01% p = 0.73). The quality of the three mAbs was assured, suggesting that the V50 drone did not induce sufficient levels of vibration to adversely affect their quality
Accepting Optimally in Automated Negotiation with Incomplete Information (abstract)
No full textIntelligent SystemsElectrical Engineering, Mathematics and Computer Scienc
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