Effect of Microstructure on the Accelerated Creep of 20CrMoV12‐1 and P 91 Steels

In the initial part the change of microstructure for steel X20 CrMoV 121 is discussed in terms of the distribution of carbide precipitates and its effects on accelerated creep resistance and hardness are presented. In the following, experimental results of microstructure and accelerated creep resistance are presented for the steels X20CrMoV 121 and P91 annealed for up to 8760 hours at 650°C and 750°C before the testing. A similar evolution of the distribution of carbide particles of a size above 102 nm is found for both steels, while the accelerated creep resistance is diminished much stronger for the steel X20CrMoV 121. This difference is due to a greater stability of NbC than that of VC precipitates, both related to the evolution of the chemical composition of complex chromium, molybdenum and iron carbide particles.     

A formulation for near-wall RANS/LES coupling

A near-wall eddy-viscosity formulation for LES is presented. A RANS-like eddy-viscosity corrected with the resolved turbulent stress is imposed in the near-wall region. The RANS eddy-viscosity is obtained from a resolved LES of channel flow at Re_τ = 395 and stored in a look-up table. When used with a wall stress model, this technique enables LES to be performed on coarse grids. Results are presented for channel flow at several Reynolds numbers up to Re_τ = 10,000. Various issues concerning the numerical behavior of the method are discussed.     

Performance evaluation of adaptive routing algorithms in packet‐switched intersatellite link networks

This paper addresses the performance evaluation of adaptive routing algorithms in non‐geostationary packet‐switched satellite communication systems. The dynamic topology of satellite networks and variable traffic load in satellite coverage areas, due to the motion of satellites in their orbit planes, pose stringent requirements to routing algorithms. We have limited the scope of our interest to routing in the intersatellite link (ISL) segment. In order to analyse the applicability of different routing algorithms used in terrestrial networks, and to evaluate the performance of new algorithms designed for satellite networks, we have built a simulation model of a satellite communication system with intersatellite links. In the paper, we present simulation results considering a network‐uniform source/destination distribution model and a uniform source–destination traffic flow, thus showing the inherent routing characteristics of a selected Celestri‐like LEO satellite constellation. The updates of the routing tables are centrally calculated according to the Dijkstra shortest path algorithm. Copyright © 2002 John Wiley & Sons, Ltd.     

Ionic polymers with tunable liquid‐crystalline properties

Side‐chain polyesters were synthesized from N‐octyl‐, N‐dodecyl‐ or N‐hexadecyl‐diethanolamine and succinic acid anhydride. These polyesters were then transformed into polyester hydrochlorides by protonation of the amino groups using different amounts of HCl (20–100 mol%). Above 60 mol% the reaction is not quantitative and a degree of protonation of up to 88% is obtained. The structures of the synthesized polyesters and their hydrochlorides were determined by ¹H nuclear magnetic resonance spectroscopy. The thermal properties of the synthesized polyesters and their hydrochlorides were also studied using differential scanning calorimetry in relation to the side‐chain length and the degree of polyester protonation. The polyester with octyl side chains and its hydrochlorides were amorphous liquids at room temperature, while the polyester and polyester hydrochlorides with hexadecyl side chains formed a smectic crystalline phase, S_mB, or its tilted analogues. The polyester with a dodecyl side chain was also an amorphous liquid at room temperature, while its hydrochlorides with various degrees of protonation were smectic liquid crystals, as determined by X‐ray diffraction. By simply varying the degree of protonation the liquid crystal isotropization temperature was increased from 32 °C to 82 °C. Copyright © 2011 Society of Chemical Industry     

Simplified soft value extraction for M-PPM-modulated signals in FSO systems

In the following paper we propose a new approach for extracting soft values from Mth order pulse position modulation (M-PPM). A new low-complexity algorithm is developed, where soft information for each data bit is calculated based on the power received within the PPM time slots. In order to decrease the computational complexity we simplify the calculation of the conditional probability of data vector a given that PPM symbol Y is received. The Monte Carlo simulations applied to analyze the properties of the algorithm for turbo-coded M-PPM transmission in free space optic communication systems show acceptable degradation of system performance with regard to system simplification.     

Fourier transform infrared analysis of gas composition in low-volume light bulbs

Fourier transform infrared spectroscopy has been used for in situ analysis of HBr, CH3Br, and CO within light bulbs at different stages of burning time. The interference fringes originated in the quartz walls of the bulbs have been eliminated by different methods. The NIPALS procedure yielded higher S/N ratio than the fringe-elimination method applied. The CO and HBr showed time-dependent concentration changes during the burning period. The maximum CO concentration (approximately 6 ppm) was detected after 30-50 s of burning time, and then it practically burned out after 5 h. The HBr concentration increased in the first 3 min of burning, and then its concentration stabilized at a 10-15 ppm level. After 5 s of illumination, the CH3Br concentration became undetectable.     

Hybrid fuzzy model-based predictive control of temperature in a batch reactor

Processes in industry, such as batch reactors, often demonstrate a hybrid and non-linear nature. Model predictive control (MPC) is one of the approaches that can be successfully employed in such cases. However, due to the complexity of these processes, obtaining a suitable model is often a difficult task. In this paper a hybrid fuzzy modelling approach with a compact formulation is introduced. The hybrid system hierarchy is explained and the Takagi–Sugeno fuzzy formulation for the hybrid fuzzy modelling purposes is presented. An efficient method for identifying the hybrid fuzzy model is also proposed.

A MPC algorithm suitable for systems with discrete inputs is treated. The benefits of the MPC algorithm employing the proposed hybrid fuzzy model are verified on a batch-reactor simulation example: a comparison between MPC employing a hybrid linear model and a hybrid fuzzy model was made. We established that the latter approach clearly outperforms the approach where a linear model is used.     

An investigation of strengthening by spherical coherent G. P. Zones

Increases in the critical resolved shear stress of Al-Zn single crystals were measured at 77°C as a function of the volume fraction and average size of the Guinier-Preston (G.P.) zone population. Zone volume fractions ranging from 1.45 to 13 pct were studied which included average zone sizes of from 8 to 90Å. The G.P. zone sizes were determined by an X-ray small angle scattering technique developed by Harknesset al. The increase in the critical resolved shear stress was shown to be determined by the increased Zn-Al interface created by dislocation shear through the G.P. zone. The surface energy of the coherent boundary between zone and matrix was found to be 320 ergs per sq cm by this approach. Furthermore, a model based on surface creation was shown to be consistent with other general features of the deformation process.     

Solidification of Be-free Ni-based dental alloy

A novel, Nb- and Si-rich and Be-free Ni-based alloy was cast by two methods of investment casting and continuous casting to study the microstructure evolution during solidification and its mechanical properties. The solidification of the alloy started with the primary crystallization of FCC-γ, followed by a binary eutectic reaction, with the formation of a heterogeneous constituent: FCC-γ+G-phase, which replaced the low-melting eutectic (FCC-γ+NiBe) in the Be-bearing alloys. AlNi₆Si₃ and γ′ formed during the terminal stages of solidification by investment casting, while the formation of AlNi₆Si₃ was suppressed by continuous casting. The Scheil solidification model agreed very well with the experimental results.     

Spatial resolution of body surface potential maps and magnetic field maps: a simulation study applied to the identification of ventricular pre-excitation sites

Telemedicine is defined as the "delivery of health care and sharing of medical knowledge over a distance using telecommunication systems." The concept of telemedicine is not new. Beyond the use of the telephone, there were numerous attempts to develop telemedicine programs in the 1960s mostly based on interactive television. The early experience was conceptionally encouraging but suffered inadequate technology. With a few notable exceptions such as the telemetry of medical data in the space program, there was very little advancement of telemedicine in the 1970s and 1980s. Interest in telemedicine has exploded in the 1990s with the development of medical devices suited to capturing images and other data in digital electronic form and the development and installation of high speed, high bandwidth telecommunication systems around the world. Clinical applications of telemedicine are now found in virtually every specialty. Teleradiology is the most common application followed by cardiology, dermatology, psychiatry, emergency medicine, home health care, pathology, and oncology. The technological basis and the practical issues are highly variable from one clinical application to another. Teleradiology, including telenuclear medicine, is one of the more well-defined telemedicine services. Techniques have been developed for the acquisition and digitization of images, image compression, image transmission, and image interpretation. The American College of Radiology has promulgated standards for teleradiology, including the requirement for the use of high resolution 2000 x 2000 pixel workstations for the interpretation of plain films. Other elements of the standard address image annotation, patient confidentiality, workstation functionality, cathode ray tube brightness, and image compression. Teleradiology systems are now widely deployed in clinical practice. Applications include providing service from larger to smaller institutions, coverage of outpatient clinics, imaging centers, and nursing homes. Teleradiology is also being used in international applications. Unresolved issues in telemedicine include licensure, the development of standards, reimbursement for services, patient confidentiality, and telecommunications infrastructure and cost. A number of states and medical boards have instituted policies and regulations to prevent physicians who are not licensed in the respective state to provide telemedicine services. This is a major impediment to the delivery of telemedicine between states. Telemedicine, including teleradiology, is here to stay and is changing the practice of medicine dramatically. National and international communications networks are being created that enable the sharing of information and knowledge at a distance. Technological barriers are being overcome leaving organizational, legal, financial, and special interest issues as the major impediments to the further development of telemedicine and realization of its benefits.