National Centre of Scientific Research "Demokritos"

About: National Centre of Scientific Research "Demokritos" is a facility organization based out in Athens, Greece. It is known for research contribution in the topics: Computer science & Aerosol. The organization has 471 authors who have published 640 publications receiving 14478 citations. The organization is also known as: Demokritos.

Dynamic safety analysis of process systems with an application to a cryogenic ammonia storage tank

Abstract: A method for calculating the dynamic reliability of safety systems and its application to a refrigerated liquid cryogenic ammonia storage tank is presented. The method is based on the theory of Markov chains and can model dynamic phenomena of the process and its safety systems. It offers the capability of modelling realistically the competing process of repairing failed safety systems and the exceeding of safe limits by some critical physical parameters of the process. The results of the Markovian analysis are compared to those of the classical Fault Tree/Event Tree methods and it is shown that the proposed method offers a substantial improvement over the classical approach. The probability of failure from overpressure of a cryogenic ammonia storage tank depends in general on the level of the ammonia in the tank at the time of accident initiation. Assuming a uniform distribution for the ammonia level in the tank, the average upper and lower limits for the failure probability over a year provided by the FT/ET methods span three orders of magnitude [1.4×10 −1 –1.0×10 −4 ] depending on whether repair is considered or not. The proposed approach realistically determines this failure probability at 3.3×10 −3 . Additional results from specific levels of ammonia are also provided.

Large spin behavior of anomalous dimensions and short-long strings duality

Abstract: We are considering the semi-classical string soliton solution of Gubser, Klebanov and Polyakov which represents highly excited states on the leading Regge trajectory, with large spin in $AdS_5$. A prescription relates this soliton solution with the corresponding field theory operators with many covariant derivatives, whose anomalous scaling dimension grows logarithmically with the space-time spin. We explicitly derive the dependence of anomalous dimension on spin for all leading and next-to-leading orders at strong coupling. We develop an iteration procedure which, in principle, allows to derive all terms in the large spin expansion of the anomalous scaling dimension of twist two operators. Our string theory results are consistent with the conjectured "reciprocity" relation, which has been verified to hold in perturbation theory up to five loops in N=4 SYM. We also derive a duality relation between long and short strings.

The contribution of rare species to coastal phytoplankton assemblages

Abstract: Analysis of quantitative and qualitative composition of rare phytoplankton species was performed using a data set collected over a large geographic area (four eutrophic gulfs of the Aegean Sea, E. Mediterranean Sea) during 2002–2003. We examined the effects of excluding rare species on comparisons of species richness, diversity, similarity and niche breadth as well as the regional and seasonal contribution of rare species to cell abundance and carbon biomass. Overall, the total of 401 species included 182 rare species contributing 45.1% of the total species number. However, there was a considerable variation in this relationship among the other parameters, as rare species contributed only 6.4% of total cell abundance, 13.1% of total species diversity, 21.2% of total cell biovolume and 16.6% of total carbon biomass. The results showed that rarity may be a significant issue in studies detecting and quantifying phytoplankton community structure.

A Cloud-Enabled Small Cell Architecture in 5G Networks for Broadcast/Multicast Services

Abstract: The evolution of 5G suggests that communication networks become sufficiently flexible to handle a wide variety of network services from various domains. The virtualization of small cells as envisaged by 5G, allows enhanced mobile edge computing capabilities, thus enabling network service deployment and management near the end user. This paper presents a cloud-enabled small cell architecture for 5G networks developed within the 5G-ESSENCE project. This paper also presents the conformity of the proposed architecture to the evolving 5G radio resource management architecture. Furthermore, it examines the inclusion of an edge enabler to support a variety of virtual network functions in 5G networks. Next, the improvement of specific key performance indicators in a public safety use case is evaluated. Finally, the performance of a 5G enabled evolved multimedia broadcast multicast services service is evaluated.