Marine Polysaccharide Networks and Diatoms at the Nanometric Scale

Despite many advances in research on photosynthetic carbon fixation in marine diatoms, the biophysical and biochemical mechanisms of extracellular polysaccharide production remain significant challenges to be resolved at the molecular scale in order to proceed toward an understanding of their functions at the cellular level, as well as their interactions and fate in the ocean. This review covers studies of diatom extracellular polysaccharides using atomic force microscopy (AFM) imaging and the quantification of physical forces. Following a brief summary of the basic principle of the AFM experiment and the first AFM studies of diatom extracellular polymeric substance (EPS), we focus on the detection of supramolecular structures in polysaccharide systems produced by marine diatoms. Extracellular polysaccharide fibrils, attached to the diatom cell wall or released into the surrounding seawater, form distinct supramolecular assemblies best described as gel networks. AFM makes characterization of the diatom polysaccharide networks at the micro and nanometric scales and a clear distinction between the self-assembly and self-organization of these complex systems in marine environments possible.     

Challenges in using a probabilistic safety assessment in a risk informed process (illustrated using risk informed inservice inspection)

Many of the ongoing and expected uses of Probabilistic Safety Assessment (PSA)¹ create new challenges to ensuring that the resulting conclusions are valid. This paper provides a summary of some of these challenges. Work conducted by the authors on Risk-Informed Inservice Inspection (RI-ISI) is used to illustrate these challenges. Means to address all of the challenges are not provided in detail in this paper. Several earlier papers discuss how these challenges can be addressed. References are provided for the interested reader (Chapman JR et al. In: PSA '95, vol. 1, Seoul, 1995: 177–80; Chapman JR et al. In: ICONE-IV, New Orleans, 1996; Dimitrijevic VB et al. In: Croatian Nuclear Society International Conference, Opatija, 1996: 245–54; Dimitrijevic VB et al. In: Croatian Nuclear Society International Conference, Opatija, 1996: 255–62; Dimitrijevic VB. In: Yugoslav Nuclear Society Conference, Belgrade, 1996: 53–61; O'Regan PJ et al. In: PSA '95, Seoul, vol. 1, 1995: 403–5; O'Regan PJ. In: ICONE-IV, vol. 5, New Orleans, 1996: 277–80).     

Performance Analysis of Nonlinear Energy‐Harvesting DF Relay System in Interference‐Limited Nakagami‐m Fading Environment

A decode‐and‐forward system with an energy‐harvesting relay is analyzed for the case when an arbitrary number of independent interference signals affect the communication at both the relay and the destination nodes. The scenario in which the relay harvests energy from both the source and interference signals using a time switching scheme is analyzed. The analysis is performed for the interference‐limited Nakagami‐m fading environment, assuming a realistic nonlinearity for the electronic devices. The closed‐form outage probability expression for the system with a nonlinear energy harvester is derived. An asymptotic expression valid for the case of a simpler linear harvesting model is also provided. The derived analytical results are corroborated by an independent simulation model. The impacts of the saturation threshold power, the energy‐harvesting ratio, and the number and power of the interference signals on the system performance are analyzed.     

Synthesis and characterization of hafnium carbide fine powders

Hafnium carbide powder was synthesized by sol–gel polycondensation of hafnium chloride with citric acid. The starting materials were dissolved in water and mixed homogeneously on a hot plate until precursor gel was formed. Pyrolysis of this gel resulted in monoclinic hafnia which after subsequent heat treatment transformed into hafnium carbide. The obtained materials were analyzed by means of X-ray diffraction and scanning electron microscopy. The results showed that the obtained carbide powders were composed of nearly equiaxed particles with narrow size distribution. Characterization by nitrogen adsorption showed that the obtained powders were micro- and mesoporous materials with high specific surface area.     

Preliminary management and optimization of a gas reservoir in central Serbia

Management of hydrocarbon reservoirs is a dynamic, continuous and complex process. It is applied from reservoir discovery to its abandonment, with the objective of achieving maximum profitability by using a recovery process with minimum capital investments and operation costs.The goals of modern system-engineer' approach to hydrocarbon reservoir management are: managing efficiency; adequate and on time decision making; increasing reserves, and oil and gas recovery factor; production increment; risk reduction; investment efficiency; minimizing costs and environmental protection.The gas reservoir “M” is the gas reservoir discovered in central part of Serbia. It was not put in production yet, so it is important to apply reservoir management concepts from the beginning of the production process.Based on production characteristics, this reservoir belongs to a group of smaller gas reservoirs that characterizes most often the Serbian exploitation area. Also, this reservoir fullfils most of criteria for using it as an underground gas storage reservoir. Thus, the analysis of possibilities for conversion into the underground gas storage after certain production period was also considered.The management of gas reservoir “M” has been analyzed by two different approaches. The first one refers to the management of the reservoir as a gas producer during the whole reservoir life. The second management approach considers gas production for a certain period of time, followed by underground gas storage (UGS). In this paper, economic and financial evaluation results are given for the presented options of gas reservoir management.A decision analysis has been applied to select an optimized gas reservoir management approach.Adequate management of this gas reservoir would contribute to further development and reform of Serbia's gas energy sector that is characterized by great dependence on natural gas imports, and a lack of underground gas storage.