A Finite Element Computational Method for Gas Hydrate. Part I: Theory

A finite element scheme is presented to model the dissociation of gas hydrates in porous media by hot water injection. We show a complete derivation of the finite element formulation, including the associated mass and energy conservation equations capable of performing transient analysis of both conductive and convective heat transfer for gas and liquid flow in porous media. The scheme also includes the latent heat effect to accommodate the change of phase due to melting of hydrate. In the companion paper, Part II, this method is successfully applied to hydrate reservoirs.     

Exploiting information theory for adaptive mobility and resource management in future cellular networks

We utilize tools from information theory to develop adaptive algorithms for two key problems in cellular networks: location tracking and resource management. The use of information theory is motivated by the fundamental observation that overheads in many aspects of mobile computing can be traced to the randomness or uncertainty in an individual user's movement behavior. We present a model-independent information-theoretic approach for estimating and managing this uncertainty, and relate it to the entropy or information content of the user's movement process. Information-theoretic mobility management algorithms are very simple, yet reduce overhead by /spl sim/80 percent in simulated scenarios by optimally adapting to each individual's movement. These algorithms also allow for flexible tradeoff between location update and paging costs. Simulation results demonstrate how an information-theory-motivated resource provisioning strategy can meet QoS bounds with very small wastage of resources, thus dramatically reducing the overall blocking rate.     

Detection and analysis of transition from annular to intermittent flow in vertical tubes

In vertical co-current gas-liquid flow, the transition from annular to intermittent flow occurs when gas core becomes interrupted by liquid bridges due to the instability of the interfacial capillary waves. An analytical model is formulated to explain the liquid bridging in terms of the growth of finite amplitude interfacial capillary waves. Experimental results show that the longest wave length, which is associated with the transition, is about eight times the wave length of waves moving with the velocity of the liquid film.     

Periodic discrete-time systems: stability analysis and robustcontrol using zero placement

A simple method (based on Floquet theory) for obtaining the characteristic equation (and hence stability) of periodic discrete-time systems is presented. Using this method it is shown that 2-periodic controllers can be used to relocate the zeros of SISO plants. Some examples are considered to illustrate the use of 2-periodic controllers for robust control of finite gain margin problems     

Analysis of a TEM Cell with Septum on a Dielectric Slab

A quasi-TEM approach based on conformal transformation is used for the determination of the characteristic impedance of a rectangular coaxial line (TEM cell) having a symmetrically located inner conductor (septum) supported on a dielectric slab of equal width. The method of determination of the capacitance of the dielectric-filled portion is discussed. The results on characteristic impedance for two values of dielectric constant are presented.