EFFECT OF MASS FLUX AND SYSTEM PRESSURE ON TWO-PHASE FRICTION MULTIPLIER

A horizontal boiling water loop was used to obtain pressure drop and heat transfer data for two-phase steam-water flow for pressures of up to 825 kPa. The data were used to examine the predictions of the separated flow model using the Lockhart-Martinelli method of estimating the two-phase friction multiplier.

The influence of mass flux on the two-phase friction multiplier has been reported for high pressure systems by many workers. The present work confirms the existence of this influence at low pressures as well. System pressure is also found to be a parameter. A correlation for the two-phase friction multiplier, incorporating the effects of mass flux and pressure, is presented here. The correlation has been tested against data from two independent sources. The predictions have been found to be in very good agreement with the data.     

Layout optimization of trusses using improved GA methodologies

Summary The main concern of the paper is the simultaneous treatment of size, shape and topology variables in the optimum design of space trusses. As compared to only size optimization, this is a challenging, more difficult and complex problem. The paper discusses a solution algorithm which is based on the use of GAs. Two new methodologies, annealing perturbation and adaptive reduction of the design space, are introduced in conjunction with GAs, bringing additional increase in computational efficeiency. Some common problems in handling shape and topology design considerations are eliminated, which in turn provides a large and a flexible design environment. A numerical problem is presented to test the performance of the proposed methodologies and to compare the results with those existing in the literature. Furthermore, the paper studies a second problem designed to observe the efficiency of GAs in a considerably large and complex design space.     

Effects of interface style on user perceptions and behavioral intention to use computer systems

This study examines the influence of two interface styles (menu- and command-based) on the perceived ease of use, perceived usefulness, and behavioral intention of the user to use the system. We have treated the system interface style as an external factor in the technology acceptance model (TAM) to examine its direct and indirect effects on behavioral intention to accept and use a system. The results showed that the interface style had direct effects on perceived ease of use and perceived usefulness which, in turn, demonstrated significant effects on behavioral intention to use the system. Further, the results showed that perceptions of the menu-based interface were more favorable than perceptions of the command-based interface. These results provide several theoretical and practical implications for designing an effective system.     

A CMOS DCO design using delay programmable differential latches and a novel digital control scheme

A novel 16-bit CMOS digitally controlled oscillator (DCO) is described. This CMOS DCO design is based on a delay programmable differential latch and a novel digital control scheme which yields improved phase noise characteristics. Simulations of a 4-stage CMOS DCO using the 0.5 μm Agilent CMOS process parameters achieved a controllable frequency range of 750 MHz–1.6 GHz with a monotone tuning range of around 1 GHz. Monte Carlo simulations indicate that the time-period jitter due to random supply voltage fluctuations is under 250 ps for worst-case considerations. Also, phase noise was found to be in the range of −175 dBc at a frequency of 600 KHz from the carrier at 1.5 GHz (for digital control word of 1512 H) after numerous iterations of Monte Carlo simulations. FFT analysis indicate a total harmonic distortion (THD) of around − 57 dB for the DCO output signal. This CMOS design would thus provide considerable performance enhancement in digital PLL applications.     

Numerische Strömungssimulation an einer Niedergeschwindigkeits-Axialturbine unterschiedlichen Deckband-Abschirmungen des Laufrades

The numerical simulation of the flow through a low-speed turbine stage followed by a vane row is presented for two experimentally investigated shrouds of different weight and shape. The aerofoil-pressure distribution of the blades and vanes as well as the flow at the exit of the bladerow is compared in the experimentally and numerically obtained results. In addition to experimental data published earlier, numerical flow results are added, which had been inaccessible in the experiment. The choice of the turbulence model influences substantially the result of the numerical simulation for the flow leaving the rotor blade row. Furthermore the computational result shows the influence of the flow pattern in the labyrinth cavity on the power loss. The prediction of the static pressure decrease along the flow path through the seal across the cavities concludes this investigation.     

Dynamic stability of cracked multi-bay frame structures

The effects of crack depth and crack location on the in-plane static and dynamic stability of cracked multi-bay frame structures subjected to periodic loading have been investigated numerically by using the finite element method. For the rectangular cross-section beam, a crack element is developed by using the principles of fracture mechanics. In addition, the effect of the number of spans and static and dynamic load parameters on static and dynamic stability analysis are also investigated. For buckling and dynamic stability analyses, the results obtained by using the present model are presented in three-dimensional graphical forms and tables.     

Optimizing decomposition of software architecture for local recovery

The increasing size and complexity of software systems has led to an amplified number of potential failures and as such makes it harder to ensure software reliability. Since it is usually hard to prevent all the failures, fault tolerance techniques have become more important. An essential element of fault tolerance is the recovery from failures. Local recovery is an effective approach whereby only the erroneous parts of the system are recovered while the other parts remain available. For achieving local recovery, the architecture needs to be decomposed into separate units that can be recovered in isolation. Usually, there are many different alternative ways to decompose the system into recoverable units. It appears that each of these decomposition alternatives performs differently with respect to availability and performance metrics. We propose a systematic approach dedicated to optimizing the decomposition of software architecture for local recovery. The approach provides systematic guidelines to depict the design space of the possible decomposition alternatives, to reduce the design space with respect to domain and stakeholder constraints and to balance the feasible alternatives with respect to availability and performance. The approach is supported by an integrated set of tools and illustrated for the open-source MPlayer software.     

Formal Reasoning About Finite-State Discrete-Time Markov Chains in HOL

Markov chains are extensively used in modeling different aspects of engineering and scientific systems, such as performance of algorithms and reliability of systems. Different techniques have been developed for analyzing Markovian models, for example, Markov Chain Monte Carlo based simulation, Markov Analyzer, and more recently probabilistic model-checking. However, these techniques either do not guarantee accurate analysis or are not scalable. Higher-order-logic theorem proving is a formal method that has the ability to overcome the above mentioned limitations. However, it is not mature enough to handle all sorts of Markovian models. In this paper, we propose a formalization of Discrete-Time Markov Chain (DTMC) that facilitates formal reasoning about time-homogeneous finite-state discrete-time Markov chain. In particular, we provide a formal verification on some of its important properties, such as joint probabilities, Chapman-Kolmogorov equation, reversibility property, using higher-order logic. To demonstrate the usefulness of our work, we analyze two applications: a simplified binary communication channel and the Automatic Mail Quality Measurement protocol.