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.     

Coupled bending–torsional dynamic stiffness matrix for axially loaded beam elements

Analytical expressions for the coupled bending–torsional dynamic stiffness matrix elements of an axially loaded uniform beam element are derived in an exact sense by solving the governing differential equations of motion of the beam. The influence of axial force on the coupled bending–torsional frequencies of a cantilever and hinged–hinged beam of thin-walled section is demonstrated by numerical results. Application of the developed theory includes coupled bending–torsional frequency and mode calculations of helicopter, turbine and propeller blades, plane and space frames, and grillages consisting of axially loaded beam elements with non-coincident mass centre and shear centre.     

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.     

Effect of epitaxial realignment on the leakage behavior of arsenic-implanted,as-deposited polycrystalline Si-on-single crystal Si diodes

When dopants are indiffused from a heavily implanted polycrystalline silicon film deposited on a silicon substrate, high thermal budget annealing can cause the interfacial “native” oxide at the polycrystalline silicon-single crystal silicon interface to break up into oxide clusters, causing epitaxial realignment of the polycrystalline silicon layer with respect to the silicon substrate. Anomalous transient enhanced diffusion occurs during epitaxial realignment and this has adverse effects on the leakage characteristics of the shallow junctions formed in the silicon substrate using this technique. The degradation in the leakage current is mainly due to increased generation-recombination in the depletion region because of defect injection from the interface.     

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     

Elastic stress analysis of three-dimensional solids with small holes by BEM

An advanced level development of the boundary element method is presented for the elastic stress analysis of a three-dimensional solid containing a large number of small diameter, tubular shaped holes. The formulation has been developed such that these holes can be modelled by a system of curvilinear line elements, resulting in substantial savings in both data preparation and computing costs. This is accomplished by assuming a variation in the displacement field along the circumference defined in terms of trigonometric functions together with a linear or quadratic variation of displacements along the longitudinal direction.     

A comparison between isoparametric Lagrangian elements in 2D BEM

A comparison between a family of isoparametric C°-continucus elements in the context of two-dimensional elastostatics using the direct boundary element method is presented. The elements studied use Lagrangian shape functions of orders quadratic, cubic and quartic. The relative efficiencies of these elements from the viewpoint of accuracy of solution as well as cost effectiveness are examined through certain selected problems. It emerges from the present study that the quartic element is more reliable in accuracy than the lower members of the family without being necessarily more expensive.     

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.