Dynamic aspects of voltage/power characteristics [multimachinepower systems]

The authors investigate the dynamic aspects of operation on a typical voltage/power curve. They discuss multiple stable equilibrium points in the context of small signal stability. A single machine example supplying different types of voltage-dependent loads is examined. A multimachine power system is also studied. Examples include a discussion on multiple stable operating points and the effects of different load characteristics     

Characterization of simulated microstructures in polydisperse particle deposition

The deposition of polydisperse particles under the influence of gravity is examined using computer simulation. A parameter, σ, that represents the standard deviation of particle size is used for studying the effect of the variation in polydispersity on the resulting microstructures. Structural correlations are examined through contact networks, radial and angular distribution functions, and diffraction patterns. The results show that the onset of ordering appears near σ = 0.05 as σ is decreased. The long-range ordering of the structures is not influenced by the introduction of a small amount of polydispersity, which may increase the uniformity of local density distribution in the angular direction. Polydisperse systems with small deviations in size display stronger positional order in some directions and this in turn contributes to the uniformity of overall packing structures.     

The usefulness of static condensation in the finite element analysis of stiffened submersible cylindrical hulls

The usefulness of the static condensation technique in the finite element analysis of stiffened submersible. cylindrical hulls is examined in this paper. The finite element formulation used herein is essentially the same as outlined by the authors in an earlier paper wherein the stiffener is modeled rigorously using axisymmetric thin annular plate elements for the web and axisymmetric thin shell elements for the flange. The static condensation technique has been applied in this paper to reduce these stiffener finite elements so that their effect can be transferred to the shell node at the point of attachment of the stiffener with the shell. The advantage of such condensation of the stiffener elements is the smaller number of equations to be solved without the rigor of the stiffener modeling being lost in any way. The manner of incorporating the condensation in the computer program has been described. Examples of several stiffened submersible cylindrical hulls have been considered as an illustration of the use of the program.     

Electrochemical preparation of potassium gold cyanide

The essential requirements for the industrial preparation of potassium gold cyanide (pgc) are: (a) high rate of dissolution and (b) smooth and uniform dissolution. Employing galvanostatic and potentiostatic polarisation data and observations on the surface topography of anodes dissolved by both the techniques, it is shown that potentiostatic dissolution of gold in potassium cyanide at +0·345 V satisfies the above requirements.     

Sulphonated polyisobutylene telechelic ionomers: 12. Solid-state mechanical properties

The solid-state mechanical properties of well defined sulphonated polyisobutylene telechelic ionomers are presented. Specifically, the effect of (1) molecular architecture, (2) molecular weight, (3) type of cation used for neutralization and (4) excess neutralizing agent has been investigated. In addition, the effect of moisture and ionic plasticizer on the stress-strain behaviour has also been studied.

These ionomers do not display the characteristic small-angle X-ray scattering (SAXS) peak, which is indicative of the presence of clusters, above a number-average molecular weight of about 10 000. However, below this molecular weight a weak shoulder is sometimes observed on the SAXS curve. The tri-arm species form a network structure at ambient temperatures which results in materials with good mechanical properties. The mechanical properties of the linear difunctional species are inferior to those of the three-arm star trifunctional species due to a less well developed network structure. The monofunctional species are very tacky at ambient temperatures and cannot be handled as solid materials. However, by their incorporation into the trifunctional systems they do serve as a model for ‘dangling ends’. As expected, these blends display significantly different properties than those possessed with the pure trifunctional species.

Addition of excess neutralizing agent significantly increases the high deformation properties with little effect on Young's modulus. A simple morphological model has been postulated in which it is suggested that the excess neutralizing agent resides at the ionic sites rather than being uniformly distributed throughout the matrix. Zinc-neutralized ionomers show stress-strain behaviour which is comparable to the potassium- and calcium-neutralized materials at ambient conditions, but the softening temperature is lower for the zinc neutralized material. Water absorption in these materials is relatively low. Addition of zinc stearate, an ionic plasticizer, facilitates melt processing by lowering the viscosity at high temperatures yet at ambient temperatures it crystallizes and acts as a reinforcing filler thus increasing Young's modulus.     

Phone number portability for PCS systems with ATM backbones usingdistributed dynamic hashing

Current cellular subscribers have a geographic phone number (e.g., in AMPS and US digital cellular systems) or a number which contains the network provider's identity (e.g., in GSM), and whenever subscribers register or receive (and possibly, originate) a call, a home location register (HLR) database has to be queried. The wired infrastructure supports a function called global title translation (GTT) that converts the subscriber's number to an HLR database address. A special feature of next generation wireless access service will be to support personal communication services (PCS) and wireless subscribers with portable personal numbers, or nongeographic phone numbers (NGPNs), that do not indicate the service provider or HLR database serving the user. In addition, the GTT function may not be available when the wired backbone is an ATM network. Thus a key function required in future wireless access systems with wired ATM backbones will be the ability to translate an NGPN to the identity of the HLR which serves the subscriber, a process we call NGPN translation. We discuss the requirements of NGPN translation and some alternative schemes. We propose two schemes for fast, efficient, scalable and flexible NGPN translation which use ideas of dynamic hashing, caching, and indirection. The schemes use a hash function in the visiting location registers (VLRs) (or serving SCP) and a set of distributed translation servers which store the NGPN-to-HLR mapping. We discuss how the operations required to maintain the translation information can be performed. Finally, we perform a simplified analysis of the scalability of the alternative schemes as well as the hash-based schemes we propose     

H-phosphonate derivatives as novel peptide deformylase inhibitors

Peptide deformylase catalyzes the removal of the N-terminal formyl group from nascent polypeptides during prokaryotic protein maturation and is essential for bacterial survival. Its absence from eukaryotic organisms makes it an attractive target for designing novel antibacterial agents. Peptidyl H-phosphonates were synthesized and shown to be competitive inhibitors of the deformylase.     

Improving electromigration reliability in Al-alloy lines

We present a method that utilizes surface topography to control the distribution of grain sizes, single grain segment lengths and polygrain cluster lengths in Al---Cu thin films. Microstructural data for the grain size and segment/cluster length distribution parameters are presented that demonstrate the influence of various topographical features adjacent to conductor lines. Experimental results show the impact of these features on electromigration failure times. Our results demonstrate that the relationship between median failure time and segment length is consistent with the critical threshold length concept for long interconnects containing large numbers of single grain segments and polygrain clusters. These results demonstrate the importance of the segment length and type in controlling electromigration mass transport.     

On plastic strain recovery in freestanding nanocrystalline metal thin films

In a recent article [J. Rajagopalan, J.H. Han, M.T.A. Saif, Science 315 (2007) 1831–1834], we have reported substantial (50–100%) plastic strain recovery in freestanding nanocrystalline metal films (grain size 50–65 nm) after unloading. The strain recovery was time dependent and thermally activated. Here we model the time evolution of this strain recovery in terms of a thermally activated dislocation propagation mechanism. The model predicts an activation volume of ≈42b³ for the strain recovery process in aluminum.     

Image restoration using the particle filter: handling non-causality

A recursive-state estimation scheme for image restoration using the particle filter is described. Handling non-causal blurs within a recursive framework is a challenging problem. Most recursive image restoration schemes assume the blur to be causal or semi-causal in nature, but this is unrealistic. A novel choice for the state vector and a concurrent block estimation technique to incorporate full-plane regions of support for the image model as well as the blur are proposed. The particle filter-based framework enables general types of degradations to be tackled. The method assumes that the functional form of the distortion as well as the noise statistics are known but does not place any restrictions on them. Several experimental results are presented to validate the approach