Computation of the Hessian matrix in aerodynamic inverse design using continuous adjoint formulations

Continuous adjoint formulations for the computation of (first and) second order derivatives of the objective function governing inverse design problems in 2D inviscid flows are presented. These are prerequisites for the use of the very efficient exact Newton method. Four new formulations based on all possible combinations of the direct differentiation method and the continuous adjoint approach to compute the sensitivity derivatives of objective functions, constrained by the flow equations, are presented. They are compared in terms of the expected CPU cost to compute the Hessian of the objective function used in single-objective optimization problems with N degrees of freedom. The less costly among them was selected for further study and tested in inverse design problems solved by means of the Newton method. The selected approach, which will be referred to as the direct-adjoint one, since it performs direct differentiation for the gradient and, then, uses the adjoint approach to compute the Hessian, requires as many as N+2 equivalent flow solutions for each Newton step. The major part of the CPU cost (N equivalent flow solutions) is for the computation of the gradient but, fortunately, this task is directly amenable to parallelization. The method is used to reconstruct ducts or cascade airfoils for a known pressure distribution along their solid boundaries, at inviscid flow conditions. The examined cases aim at demonstrating the accuracy of the proposed method in computing the exact Hessian matrix as well as the efficiency of the exact Newton method as an optimization tool in aerodynamic design.     

Inter-agent Dialogues in Electronic Marketplaces

This paper presents an overall framework for carrying out different types of dialogues between intelligent and autonomous agents acting in an electronic marketplace. Such dialogues take place during various commercial transactions concerning requests and offers of products and services. The proposed dialogue framework has been adopted in the communication and collaboration protocols of an already implemented system, which enables buyers and sellers delegate a variety of tasks to their personal agents. Much attention has been paid to the personalization of collaborative agents, which may permanently live and interact in the market representing their owners' interests. Our overall approach builds on a modular decomposition of the agents involved, and a formal and operational modeling of the associated dialogues. Features of our framework are demonstrated through an illustrative example of dialogues deployed during interagent transactions on the establishment of a combined reservation for dinner and a movie. The main contribution of this work is that the proposed framework is capable to represent disparate dialogues taking place among agents having adopted diverse strategies for carrying out e-commerce transactions.     

Effect of copper additions on the isothermal bainitic transformation in hypereutectoid copper and copper-nickel steels

During the isothermal bainitic transformation in hypereutectoid steels alloyed with copper or copper and nickel, it was found that at all the transformation temperatures studied, the formation of equally copper supersaturated bainitic ferrite and cementite always occurred. This observation implies the formation of bainitic ferrite and cementite from the parent austenite phase without redistribution of the alloying elements, since the solubility of copper in cementite is negligible and very low in bainitic ferrite. By carefully designing suitable tempering treatments, it is possible to produce copper precipitation not only within tempered bainitic ferrite in both types of steel using low tempering temperatures, but also within the tempered bainitic cementite of the copper steel at higher tempering temperatures. The interpretation of these experimental data strongly supports the theory that bainite formation is promoted through a shear controlled type of mechanism.     

A new approach to the design of reinforcement schemes for learningautomata: stochastic estimator learning algorithms

A new class of learning automata is introduced. The new automata use a stochastic estimator and are able to operate in nonstationary environments with high accuracy and a high adaptation rate. According to the stochastic estimator scheme, the estimates of the mean rewards of actions are computed stochastically. So, they are not strictly dependent on the environmental responses. The dependence between the stochastic estimates and the deterministic estimator's contents is more relaxed when the latter are old and probably invalid. In this way, actions that have not been selected recently have the opportunity to be estimated as “optimal”, to increase their choice probability, and, consequently, to be selected. Thus, the estimator is always recently updated and consequently is able to be adapted to environmental changes. The performance of the Stochastic Estimator Learning Automaton (SELA) is superior to the previous well-known S-model ergodic schemes. Furthermore, it is proved that SELA is absolutely expedient in every stationary S-model random environment     

Simulation of two-phase flows in vertical tubes with the CTFD code FLUBOX

The computational two-fluid dynamics (CTFD) code FLUBOX is developed at GRS for the multidimensional simulation of two-phase flows. The single-pressure two-fluid model is used as basis of the simulation. A basic mathematical property of the two-fluid model of FLUBOX is the hyperbolic character of the advection. The numerical solution methods of FLUBOX make explicit use of the hyperbolic structure of the coefficient matrices. The simulation of two-phase flow phenomena needs, apart from the conservation equations for each phase, an additional transport equation for the interfacial area concentration. The concentration of the interfacial area is one of the key parameters for the modeling of interfacial friction forces and interfacial transfer terms. A new transport equation for the interfacial area concentration is in development. It describes the dynamic change of the interfacial area concentration due to mass exchange and a force balance at the phase boundary. Results from FLUBOX calculations for different experiments of two-phase flows in vertical tubes are presented as part of the validation.     

Pax7 includes two polymorphic homeoboxes which contain rearrangements associated with differences in the ability to regenerate damaged skeletal muscle in adult mice

Pax7 is a paired-type homeobox gene which has previously been shown to play an important role in skeletal muscle formation. It is expressed in skeletal muscle of the limbs during embryogenesis and in adulthood. The aims of this study were firstly to determine the degree of polymorphism of Pax7 amongst inbred laboratory mice using Southern blotting and Pax7 regional specific sub-probes. Secondly, functional studies were performed on mice with each of the different structural forms of Pax7 to determine whether they were associated with differences in the ability to regenerate damaged skeletal muscle. Four different allelic forms of Pax7 have now been identified in laboratory mice indicating that the previously reported DNA sequence of Pax7 is not applicable to all laboratory mice. Hybridisation patterns of TaqI digested DNA representing each of the different Pax7 alleles with the Pax7 specific sub-probes suggested that in contrast to previous findings, Pax7 is associated with two highly polymorphic homeoboxes. The presence of two homeoboxes in BALB/c mice has been confirmed by DNA sequencing. Results of functional studies have also shown that the ability to regenerate damaged skeletal muscle in adult mice is strongly associated with the presence of a 0.15-kb TaqI fragment derived from one of the homeoboxes.     

Learning automata-based bus arbitration for shared-medium ATM switches

Although new high-bandwidth network technologies are being introduced and widely deployed, asynchronous transfer mode (ATM) is still considered one of the most important network technologies currently in use. A number of ATM switch architectures have been proposed in the literature. However, industry has shown that is better to use the well-known shared-medium technique in the design of these ATM switches. In this paper, four variations of a new distributed scheme are proposed for the arbitration of a shared bus of an ATM switch. These schemes are based on learning automata. By taking advantage of the bursty nature of ATM traffic, the new arbitration scheme demonstrates superb performance compared to the time division multiple access (TDMA) scheme.     

Monitoring Water Quality and Assessment of Land-Based Nutrient Loadings and Cycling in Kavala Gulf

The results of a systematic and intensive nutrient monitoring program are reported, which took place during the period 1997–1999 in Kavala Gulf, Northern Greece, having as a general task to study the impact of the various human activities on the nutrient loadings and cycling of the aquatic environment. A nutrient budget box model was used to estimate the annual capacity of Kavala Gulf to store and transform dissolved inorganic nitrogen and phosphorus, aiming at understanding the biogeochemical processes taking place in the area of interest. Point sources of nutrients from two municipal wastewater treatment plants (Kavala and Palio Seawage Treatment Works) and a phosphoric fertilizer producing industrial facility (PFP), as well as non-point sources from agricultural activities, seem responsible for the increased concentrations of dissolved inorganic nitrogen and phosphorus. Seasonal N:P-ratios suggest that nitrogen is the limiting nutrient during the summer, autumn and winter and phosphorus during the spring. The annual nutrient budget model revealed that Kavala Gulf is presently slightly autotrophic with nitrogen fixation exceeding denitrification.     

Photovoltaic properties of sputtered n-CdO films on p-Cu2O

The heterojunction CdO/Cu₂O was prepared by sputtering CdO films on Cu₂O at room temperature. The optical transmission of CdO films at a thickness of ≈1000 Å was ≈85%. The analysis of the I–V characteristics at different temperatures gave information of the carrier transport mechanism at the junction. The forward and the reverse dark current is dominated by a tunneling process. Measurements of the open-circuit photovoltage resulted in a curve which indicates a sensitivity range from 2.25 to 2.48 eV, similar to that found in Cu₂O MIS solar cells.