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RISS 인기검색어
- 검색키워드
- 저자 : Bednar, Michal (검색결과 6 건)
- 무료
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Comparison of waveform inversion, part 2: phase approach
Bednar, J. B.,Shin, Changsoo,Pyun, Sukjoon unknown 2007 Geophysical prospecting Vol.55 No.4
<P>ABSTRACT</P><P>In this paper, we take advantage of the natural separation into amplitude and phase of a logarithmic-based approach to full-wavefield inversion and concentrate on deriving purely kinematic approaches for both conventional and logarithmic-based methods. We compare the resulting algorithms theoretically and empirically. To maintain consistency between this and the previous paper in this series, we continue with the same symbolism and notation and apply our new algorithms to the same three data sets. We show that both of these new techniques, although different in implementation style, share the same computational methodology. We also show that reverse-time back-propagation of the residuals for our new kinematic methods continues to be the basis for calculation of the steepest-descent vector. We conclude that the logarithmic phase-based method is more practical than its conventionally based counterpart, but, in spite of the fact that the conventional algorithm appears unstable, differences are not great.</P>
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Birgit Bednar-Friedl,KARL FARMER 한국국제경제학회 2012 International Economic Journal Vol.26 No.2
In view of still large external imbalances across the world economy and dramatically risen public debts in major advanced economies, this paper reconsiders the relationship between public debt, the terms of trade and welfare in a two-good, two-country overlapping generations model with technological differences across countries. We find that the terms of trade effect of a public debt shock depends only on international differences in capital production shares and the dynamic (in)efficiency of the world economy. As in a model with similar capital production shares, domestic welfare rises and foreign welfare decreases when Home has a positive external balance and the Golden Rule holds. Under dynamic efficiency, welfare decreases in the debt-expanding, net foreign creditor country if she has a relatively smaller capital production share, and if the welfare effect through the accumulation channel is negative. In contrast, under dynamic inefficiency she can increase her welfare by debt expansion.
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Comparison of waveform inversion, part 3: amplitude approach
Pyun, Sukjoon,Shin, Changsoo,Bednar, J. B. unknown 2007 Geophysical prospecting Vol.55 No.4
<P>ABSTRACT</P><P>In the second paper of this three part series, we studied the case of conventional and logarithmic phase-only approaches to full-waveform inversion. Here, we concentrate on deriving amplitude-only approaches for both conventional- and logarithmic-based methods. We define two amplitude-only objective functions by simply assuming that the phase of the modelled wavefield is equal to that of the observed wavefield. We do this for both the conventional least-squares approach and the logarithmic approach of Shin and Min. We show that these functions can be optimized using the same reverse-time propagation algorithm of the full conventional methodology. Although the residuals in this case are not really residual wavefields, they can both be considered and utilized in that sense. In contrast to the case for our phase-only algorithms, we show through numerical tests that the conventional amplitude-only inversion is better than the logarithmic method.</P>
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Intracranial Pressure and Experimental Model of Diffuse Brain Injury in Rats
Blaha, Martin,Schwab, Juraj,Vajnerova, Olga,Bednar, Michal,Vajner, Ludek,Michal, Tichy The Korean Neurosurgical Society 2010 Journal of Korean neurosurgical society Vol.47 No.1
Objective: In this study, we present a simple closed head injury model as a two-stage experiment. The height of the weight drop enables gradation of head trauma severity. Methods: The head injury device consists of three parts and there are three adjustable parameters-weight (100-600 g). height of fall (5-100 cm) and elasticity of the springs. Thirty male Wistar rats underwent monitoring of intracranial pressure with and without induction of the head injury. Results: The weight drop from 45 to 100 cm led to immediate seizure activity and early death of the experimental animals. Severe head injury was induced from 40 cm weight drop. There was 50% mortality and all surviving rats had behavioral deterioration. Intracranial pressure was 9.3${\pm}$3.76 mmHg. Moderate head injury was induced from 35 cm, mortality decreased to 20-40%, only half of the animals showed behavioral pathology and intracranial pressure was 7.6${\pm}$3.54 mmHg. Weight drop from 30 cm caused mild head injury without mortality and neurological deterioration. Intracranial pressure was slightly higher compared to sham group- 5.5${\pm}$0.74 mmHg and 2.9${\pm}$0.81 mmHg respectively. Conclusion: This model is an eligible tool to create graded brain injury with stepwise intracranial pressure elevation.
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K. Mouralova,L. Benes,J. Bednar,R. Zahradnicek,T. Prokes,R. Matousek,P. Hrabec,Z. Fiserova,J. Otoupalik 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.5
Wire electrical discharge machining (WEDM) is an unconventional machining method for manufacturing complex-shaped, precise components. Considering the high-energy intensity of the wire erosion process, its effective implementation requires a maximum cutting speed while still ensuring the best possible quality of the machined surface. For this latter purpose, we conducted a design of experiment (DoE) comprising 33 cycles and five input factors, or machine setting parameters: Gap voltage, pulse on time, pulse off time, discharge current, and wire feed. In this context, we statistically evaluated the cutting speed in Hadfield steel, as related to machine setting parameters, and also analyzed the machined surfaces of the applied samples. The actual experiment involved examining in detail the topography of the surfaces, using one contact and three non-contact profilers. The surface morphologies were observed via electron microscopy, and a lamella was prepared to facilitate the chemical composition analysis (EDX) with a transmission electron microscope (TEM). To study the subsurface layer and its defects, we produced metallographic specimens of all the samples; the items were observed by means of light and electron microscopes. With a maximum cutting speed the highest quality of the machined surface was achieved; however, the burned cavities can affect the life expectancy of the machined parts. The TEM lamella revealed that the individual alloying elements had segregated into regions, exhibiting high volumes of both manganese and the recast layer and, due to the use of WEDM, a manganese separation layer had formed at the boundary of the recast layer and the base material.
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