An analysis of laminar forced convection film boiling

A study of forced convection film boiling on a horizontal isothermal plate is made using a treatment based on boundary layer theory. For the vapour, the velocity and temperature distributions are obtained from equations of motion and energy. For the liquid layer, the Howarth approximation for flow over a plate is used. Then, by employing interface matching conditions, the significance of the rhμ ratio between the vapour and the liquid on the variation of Nusselt number is examined.     

Structural phase stability of ThSb and ThAs under pressure

The high-pressure behaviour of thorium monopnictides is of considerable interest as these systems exhibit structural phase transitions under pressure. At ambient conditions these compounds crystallize in the NaCl-type (B1) structure. Experiments show that with the application of pressure these compounds transform to the CsCl-type (B2) structure. ThSb and ThAs are found to exhibit B1–B2 transition in the pressure range between 9–12 GPa and 1826 GPa respectively. In this work, we present the electronic and high-pressure behaviour of ThAs and ThSb performed using the tight-binding linear muffin-tin orbital method. The total energies within the atomic sphere approximation were calculated as a function of volume for both the B1 and B2 structures. The total energy calculations reveal that both ThSb and ThAs are stable in the B1 structure at ambient conditions and undergo structural transition to the B2 structure at pressures 78 and 240 kbar respectively, which are in good agreement with the experimental values. The calculated values of equilibrium lattice parameter and the transition pressure are found to be in good agreement with the experimental results.     

Mobility management in wireless ATM networks

Mobile ATM offers a common wired network infrastructure to support mobility of wireless terminals, independent of the wireless access protocol. In addition, it allows seamless migration to future wireless broadband services, such as wireless ATM, by enabling mobility of end-to-end ATM connections. In spite of the diversity in mobile networking technologies (e.g., cellular telephony, mobile-IP, packet data services, PCS), all of them require two fundamental mechanisms: location management and handoff. This article describes different schemes for augmenting a wired ATM network to support location management of mobile terminals and handoff protocols for rerouting a connection data path when the endpoint moves. A prototype implementation of mobile ATM integrating mobility support with ATM signaling and connection setup, is presented. It shows how mobile ATM may be used to provide mobility support to an IP terminal using non-ATM wireless access     

Structures and phase transitions in colloidal dispersions from theory and simulation

Equilibrium properties of uncharged colloidal dispersions with particles interacting via harsh short-ranged repulsive forces and strong short-ranged attractive forces are determined by means of an approach in which colloids are treated as supramolecular versions of simple fluids. The interparticle interactions are represented by short-ranged square-well potentials. Structure factors and phase diagrams for the dispersions are determined analytically by mapping the square-well potential onto the adhesive-hard-sphere model by equating the respective second virial coefficients. Theoretical predictions are compared with molecular simulation results for the conditions relevant to real colloidal dispersions, Our results show that the ad lies adhesive-hard-sphere model can describe accurately structure factors and phase diagrams of nonionic microemulsions and inverted micellar systems containing .AOT surfactant dispersed in oil. Both upper-critical and lower-critical consolute points in colloidal dispersions dominated by short-ranged attractive forces can be described using the same formalism.Paper presented al the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

Flow in a channel rotated impulsively

Summary A study is made on the unsteady flow of a viscous and incompressible fluid in a channel bounded by two parallel plates for the two cases, (1) when it is rotated impulsively with the constant angular velocity and (2) when the rotating channel is stopped abruptly. In both cases exact solutions of the equations of motion are obtained. It is found that in the first case the steady state conditions are reached in an oscillatory manner, while this phenomenon is not found in the latter case.With 4 Figures     

RemusDB: transparent high availability for database systems

In this paper, we present a technique for building a high-availability (HA) database management system (DBMS). The proposed technique can be applied to any DBMS with little or no customization, and with reasonable performance overhead. Our approach is based on Remus, a commodity HA solution implemented in the virtualization layer, that uses asynchronous virtual machine state replication to provide transparent HA and failover capabilities. We show that while Remus and similar systems can protect a DBMS, database workloads incur a performance overhead of up to 32 % as compared to an unprotected DBMS. We identify the sources of this overhead and develop optimizations that mitigate the problems. We present an experimental evaluation using two popular database systems and industry standard benchmarks showing that for certain workloads, our optimized approach provides fast failover ( $\le $ 3 s of downtime) with low performance overhead when compared to an unprotected DBMS. Our approach provides a practical means for existing, deployed database systems to be made more reliable with a minimum of risk, cost, and effort. Furthermore, this paper invites new discussion about whether the complexity of HA is best implemented within the DBMS, or as a service by the infrastructure below it.     

A Distributed Mechanism for Handling of Adaptive/Intelligent Selfish Misbehaviour at MAC Layer in Mobile Ad Hoc Networks

Medium access control(MAC) protocols such as IEEE 802.11 are used in wireless networks for sharing of the wireless medium.The random nature of the protocol operation together with the inherent difficulty of monitoring in the open poses significant challenges.All nodes are expected to comply with the protocol rules.But,some nodes in order to gain greater benefits misbehave by not complying with the rules.One such selfish misbehavior is waiting for smaller back-off intervals when compared to the other node...