| 1. |
- Broberg, Per
(författare)
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Sample size re-assessment leading to a raised sample size does not inflate type I error rate under mild conditions.
- 2013
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Ingår i: BMC Medical Research Methodology. - : Springer Science and Business Media LLC. - 1471-2288. ; 13:Jul,19
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Tidskriftsartikel (refereegranskat)abstract
- One major concern with adaptive designs, such as the sample size adjustable designs, has been the fear of inflating the type I error rate. In (Stat Med 23:1023-1038, 2004) it is however proven that when observations follow a normal distribution and the interim result show promise, meaning that the conditional power exceeds 50%, type I error rate is protected. This bound and the distributional assumptions may seem to impose undesirable restrictions on the use of these designs. In (Stat Med 30:3267-3284, 2011) the possibility of going below 50% is explored and a region that permits an increased sample size without inflation is defined in terms of the conditional power at the interim.
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| 2. |
- Broberg, Thomas, et al.
(författare)
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Testing the Porter hypothesis : the effects of environmental investments on efficiency in Swedish industry
- 2013
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Ingår i: Journal of Productivity Analysis. - : Springer. - 0895-562X .- 1573-0441. ; 40:1, s. 43-56
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Tidskriftsartikel (refereegranskat)abstract
- The main objective of this paper is to test the Porter hypothesis by assessing static and dynamic effects of environmental policy on productivity. According to the hypothesis, stringent environmental regulations have dynamic effects on firm performance, and these effects eventually generate profits that offset the adaptation costs. We extend previous analyses by using unique data on environmental protection investments in the Swedish manufacturing industry as a proxy for environmental stringency. These data enable us to separate environmental protection investments into pollution prevention and pollution control. This distinction is crucial since the hypothesis claims that it is investments in prevention that have positive dynamic effects on firm performance. To test the hypothesis, a stochastic production frontier model is estimated where firm inefficiency is a function of investments in environmental protection. In general, we find no support for the Porter hypothesis within the time frame of our study, indicating that environmental regulations lead to efficiency losses. This result is even stronger in the harshly regulated pulp and paper industry.
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| 3. |
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| 4. |
- Garcia de la Yedra, Aitor, et al.
(författare)
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Defect strategies in Nickel Superalloys weld using active thermography
- 2014
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Ingår i: 12th International Conference on Quantitative InfraRed Thermography, 7-11/7 Bordeaux. ; , s. 1-9
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Konferensbidrag (refereegranskat)abstract
- As a result of extreme operation conditions in gas turbines, high resistance materials with excellent behaviour at high temperature are required. Alloys, such as MarM-247 nickel based superalloy, with excellent mechanical properties at very high temperature (even at 85 % of their melting point) are being used in these applications. This extraordinary behaviour is mainly due to the presence of a strengthening phase (γ’) with the following chemical composition: Ni3(Al, Ti). However, during welding these materials are susceptible to cracking and this is why weld inspections become crucial. In this work different strategies for defect detection in welds are introduced, all of them based on active thermography. The work covers aspects such as different excitation and data evaluation strategies.
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| 5. |
- Runnemalm, Anna, 1970-, et al.
(författare)
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Automatic thermography inspection of welded components with limited access
- 2014
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Ingår i: Proceedings of 6th International Symposium on NDT in Aerospace, 12-14th November 2014, Madrid, Spain. ; , s. 1-10
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Konferensbidrag (refereegranskat)abstract
- Inspection of welds with limited access puts specific requirement on the NDT-method to be used. A non-contact method without the need for special surface preparation is preferable for fast and cost efficient inspection and with the possibility of automation. Infrared thermography has been known for quite a long time and is today mainly used for NDT inspection of composite structures. The technique is based on registering the heat conduction of the material of the surface of the structure. The method requires some kind of excitation resulting in a change of heat locally in the inspected area. In the study presented in this paper, different excitation methods are evaluated, such as continuous laser, flash lamp and induction. The study also includes conditions for miniaturization andautomation of the inspection methods. For welds difficult to access, thermography is a suggested as a possible inspection method.
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| 6. |
- Runnemalm, Anna, 1970-, et al.
(författare)
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Ultraviolet excitation for thermography inspection of surface cracks in welded joints
- 2014
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Ingår i: Nondestructive Testing and Evaluation. - : Informa UK Limited. - 1058-9759 .- 1477-2671. ; 29:4, s. 332-344
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Tidskriftsartikel (refereegranskat)abstract
- Infrared thermography is a non-contact and full field inspection method which has proven to be suitable for automatic surface crack detection. For automatic analysis of the inspection results, a high signal-to-noise ratio (SNR) is required. In this paper an alternative excitation method, using ultraviolet (UV) illumination, is presented and evaluated. Artificial surface defects, so-called notches, in a titanium plate are detected both in the weld seam and in the heat affected zone. Notches with a size from 80 mm in width and 250 mm in length are detected. The SNR using UV illumination is compared with that using flash lamp excitation. The results show that UV illumination using a mercury lamp is a good alternative as excitation source for thermography when detecting surface cracks. To validate the excitation method, results from real surface cracks are included.
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