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Some Siegel Threefolds with a Calabi-Yau Model II
Freitag, Eberhard,Manni, Riccardo Salvati Department of Mathematics 2013 Kyungpook mathematical journal Vol.53 No.2
In a previous paper, we described some Siegel modular threefolds which admit a Calabi-Yau model. Using a different method we give in this paper an enlarged list of such varieties. Basic for this method is a paper of van Geemen and Nygaard. They study a variety $\mathcal{X}$ that is the complete intersection of four quadrics in $\mathbb{P}^7(\mathbb{C})$. This is biholomorphic equivalent to the Satake compactification of $\mathcal{H}_2/{\Gamma}^{\prime}$ for a certain subgroup ${\Gamma}^{\prime}{\subset}Sp(2,\mathbb{Z})$ and it will be the starting point of our investigation. It has been pointed out that a (projective) small resolution of this variety is a rigid Calabi-Yau manifold $\tilde{\mathcal{X}}$. Then we will consider the action of quotients of modular groups on $\mathcal{X}$ and study possible resolutions that admits a Calabi-Yau model in the category of complex spaces.
Some Modular Forms Related to Cubic Surfaces
E. Freitag 경북대학교 자연과학대학 수학과 2003 Kyungpook mathematical journal Vol.43 No.3
The paper contains a thorough investigation of modular forms on a certain orthogonal group of signature (2;8). Main tools are the lifting constructions of Borcherds.These results can be applied to a unitary group of signature (1;4) which occurs as sub group of the orthogonal group. This unitary group is related to cubic surfaces. Some of the results of this paper have been used without proof in a joint paper with D. Allcock: Cubic Surfaces and Borcherds Products in Commentarii Math. Helv., Vol. 77(Issue 2), 270{296, (2002).
Mechanistic model of iodine mass transfer at pool surfaces
Fischer, K.,Freitag, M.,Kang, H.S. North-Holland Pub. Co 2014 Nuclear engineering and design Vol.278 No.-
Mass transfer of molecular iodine (I<SUB>2</SUB>) at the water pool-gas interface can be modeled by means of a water surface film renewal model superimposed to the established two-film theory, where the water-side I<SUB>2</SUB> mass transfer coefficient k<SUB>w</SUB> is related to the I<SUB>2</SUB> molecular diffusivity in water D and the air-water contact time a according to The present paper describes a mechanistic approach to determine the contact time from the water flow distribution. The method makes use of a numerical simulation of the poolwater flow, and a numerical evaluation of the contact time distribution at the pool surface. Owing to the numerical treatment it can be applied to pool geometries of any kind, which makes it applicable for nuclear reactor safety studies in general k<SUB>w</SUB>=D/πa The present paper describes a mechanistic approach to determine the contact time from the water flow distribution. The method makes use of a numerical simulation of the poolwater flow, and a numerical evaluation of the contact time distribution at the pool surface. Owing to the numerical treatment it can be applied to pool geometries of any kind, which makes it applicable for nuclear reactor safety studies in general.
Thies BEINKE,Abderrahim AIT ALLA,Michael FREITAG 국제이네비해양경제학회 2017 International Journal of e-Navigation and Maritime Vol.7 No.1
This present contribution examines by means of a discrete event and agent-based simulation the potential of a joint use of resources in the installation phase of offshore wind energy. To this end, wind farm projects to be installed simultaneously are being examined, the impact of weather restrictions on the processes of loading, transport and installation are also taken into consideration, and both the wind farm specific resource allocation and the approach of a resource pool or resource sharing, respectively, are being implemented. This study is motivated by the large number of wind farms that will be installed in the future and by the potential savings that might be realized through resource sharing. While, so far, the main driver of the resource sharing approach has been the end consumer market, it has been applied in more and more areas, even in relatively conservative industries such as logistics. After the presentation of the backgrounds and of the underlying methodology, and the description of the prior art in this context, the network of the offshore wind energy installation phase will be described. This is the basis for the subsequent determination of the savings potential of a shared resource utilization, which is determined by the performance indicators such as the total installation time and degree of utilization of the resources. The results of the simulation show that weather restrictions have a significant effect on the installation times and the usage times of the resources as well as on their degree of utilization. In addition, the resource sharing approach, has been identified to have significant savings potential for the offshore wind energy installation.
Thies BEINKE,Annabell SCHAMANN,Michael FREITAG,Klaas FELDMANN,Matthias BRANDT 국제이네비해양경제학회 2017 International Journal of e-Navigation and Maritime Vol.6 No.1
The competition of maintenance services in the offshore wind industry is continually increasing. The quality of the services acts as the distinguishing feature in the industry. Furthermore, there are public standards, which lead to the permanent necessity to offer further education and training programs for employees. To meet the requirements for further training in the specific field of application within the offshore wind industry, a gamified e-learning application has been developed and is introduced in this paper. It consists of a complete solution, which contains the automated analysis of service protocols to identify qualification needs, the involvement of service technicians in the generation of learning materials, the preparation, transmission as well as the further development of those materials in accordance with the principles of e-learning. Finally, the solution contains a gamified mobile application for qualification, which is designed to meet the individual learning needs of the service technicians. This concept paper follows a problem-centred approach. Based on the current state of technology and research, the problem and motivation are identified and the urgency is verified. Furthermore, a detailed specification of the solution and a first implementation approach is presented.
Thies BEINKE,Moritz QUANDT,Abderrahim AIT ALLA,Michael FREITAG,Thomas RIEGER 국제이네비해양경제학회 2017 International Journal of e-Navigation and Maritime Vol.8 No.1
For the German energy transition, offshore wind energy is a significant factor of success. The number of installed offshore wind energy turbines is steadily increasing. Currently, the subject matter of offshore wind energy turbine maintenance and its optimization is increasingly in the focus of research and development work. The present contribution examines the logistics of offshore wind energy turbine maintenance and the impact of the actual sea state and of sea state forecasts. To this end, the coordination processes between the players involved in the planning of service operations will be presented and analysed. Based on this, the impact of the quality of wave height forecasts on operation decisions and the mean time to repair will be determined as well as the availability of the turbines at different forecast quality levels. Proceeding on the basis of these results, the concept of a decision-making support system for operative logistics planning will be presented.
Acute Toxicity and Cytotoxicity of Pereskia aculeata, a Highly Nutritious Cactaceae Plant
Debora O. Silva,Mauricio Seifert,Fabiana R. Nora,Vera L. Bobrowski,Rogerio A. Freitag,Heidi R. Kucera,Leonardo Nora,Nilesh W. Gaikwad 한국식품영양과학회 2017 Journal of medicinal food Vol.20 No.4
Pereskia aculeata is a Cactaceae plant with valuable nutritional properties, including terrific amounts of protein, minerals, vitamins, and fiber. However, P. aculeata is reported to contain antinutrients and alkaloids in its leaves. In addition, in a study on growth and development, Wistar rats fed with P. aculeata and casein as protein source grew less than the control group (fed with casein only). Therefore, in this study, we evaluated, for the first time, the oral acute toxicity of P. aculeata in rats and also the cytotoxicity behavior of the plant on lettuce seeds. The acute toxicity research was carried out using dried P. aculeata ethanolic extract, in three different doses, administered by gavage to 24 female Wistar rats. The rats were then examined for signs of toxicity, food intake, body weight, and fecal excretion fluctuations, as well as histopathological alterations, using eight different body tissues. The acute toxicity study did not show any difference among the groups in either clinical evaluation or histopathological analyses. For the cytotoxicity study, dried P. aculeata ethanolic extract was applied on lettuce seeds in five different concentrations. These seeds were evaluated for germination, root and shoot length, and mitotic index. The results show that P. aculeata extract affects lettuce root and shoot growth, but not germination or mitotic index. In conclusion, the acute toxicity on rats and the cytogenotoxicity on lettuce of P. aculeata are neglectable, validating the potential of this plant to be used as a functional food.