Experimental analysis of a two‐axis tracking system for solar parabolic dish collector

In this paper, an attempt has been made to develop a two‐axis tracking system for solar parabolic dish concentrator and experimentally evaluated the performance of the tracking system. In this proposed design, the sensor design uses the illumination produced by the convex lens on the apex of a pyramid to align the dish in‐line with the sun. The change in incident angle of the solar rays on the lens surface shifts the area of illumination from the apex of the pyramid towards its faces. Photodiodes placed on the faces of the pyramid are used as the sensitive elements to detect the movement of the sun. The sensor output is fed to a microcontroller‐based system to drive the stepper motor on the basis of the programmed algorithm such that it receives normal incidence of sunlight on the sensor. To evaluate the performance of the proposed system, a conventional available 1‐W photovoltaic (PV) panel is placed at the focal point to measure the short circuit current and open circuit voltage. With respect to the conventional solar PV panel, it is observed that the positioning accuracy of the proposed tracking system enhances the short circuit current of 0.11 A by 86%. Thus, the proposed tracking system can be used in a stand‐alone parabolic dish with concentrating PV module as the focal point for further studies.     

Motion field modeling for video sequences

We propose a model for the interframe correspondences existing between pixels of an image sequence. These correspondences form the elements of a field called the motion field. In our model, spatial neighborhoods of motion elements are related based on a generalization of autoregressive (AR) modeling of the time-series. We also propose a joint spatio-temporal model by including spatial neighborhoods of pixel intensities in the motion model. A fundamental difference of our approach with most previous approaches to modeling motion is in basing our model on concepts from statistical signal processing. The developments in this paper give rise to the promise of extending well-understood tools of signal processing (e.g., filtering) to the analysis and processing of motion fields. Simulation results presented show the performance of our models in interframe prediction; specifically, on average the motion model performs 29% better in terms of the mean squared error energy over a commonly used pel-recursive approach. The spatio-temporal model improves the prediction efficiencies by 8% over the motion model. Our model can also be used to obtain estimates of the optical flow field as the simulations demonstrate.     

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.     

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.