Fast retrieval of similar configurations

Configuration similarity is a special form of content-based image retrieval that considers relative object locations. It can be used as a standalone method, or to complement retrieval based on visual or semantic features. The corresponding queries ask for sets of objects that satisfy some spatio-temporal constraints, e.g., "find all triplets of objects (v/sub 1/, v/sub 2/, v/sub 3/), such that v/sub 1/ is northeast of v/sub 2/, which is inside v/sub 3/." Exhaustive processing (i.e., retrieval of the best solutions) of configuration similarity queries, in general, has exponential complexity and fast search for sub-optimal solutions is the only way to deal with the vast amounts of multimedia information in several real-time applications. In this paper we first discuss the utilization of nonsystematic search heuristics, based on genetic algorithms, simulated annealing and hill climbing approaches. An extensive experimentation with real and synthetic datasets reveals that hill climbing techniques are the best for the current problem; therefore, as a subsequent step we study the search space, and develop improved variations of hill climbing that take advantage of the special structure of the problem to enhance speed. The proposed heuristic methods significantly outperform systematic search when there is only limited time for query processing.     

On asymptotically fair transmission scheduling over fading channels with measurement delay

We examine the effect of measurement delays on the throughput of certain downlink data packet systems operating over Rayleigh fading channels. In these systems the base station (BS) schedules a single user at a time and transmits at a rate which is based on measurements of the BS's received power performed by the user. The same subject was also discussed in a recent paper, titled "Asymptotically fair transmission scheduling over fading channels" by Berggren and Jantti (2004). They studied the effects of measurement delays on the operation of the scheduler. As a consequence of the delay, it is possible that by the time the BS actually transmits data, the propagation channels might have changed, such that the scheduler's choice no longer conforms to the desired scheduling policy, resulting in loss of system throughput and multi-user gain. Berggren and Jantti assume that perfect link adaptation is nevertheless always assured, i.e., that the BS transmits at a rate that matches precisely the current state of the selected user's channel. However, measurement delays lead also to mismatch between the data rate the BS transmits to the chosen user, and the current state of the propagation channel to that user. We believe that this mismatch must also be taken into account. In this letter we propose to use a backoff factor and analyze its mitigating effect on losses introduced by measurements delay in a Rayleigh fading environment. We then show the resulting gain in system throughput for optimal choices of the backoff factor     

Autothermal reforming of gasoline for fuel cell applications: Controller design and analysis

In this work, we address the control system options available to an autothermal reforming (ATR) reactor. The targeted application is within an on-board fuel processor for a hydrogen-fed low-temperature fuel cell. The feedback controller employs air feed rate as the manipulated variable and a measurement of catalyst temperature as the control variable. Disturbances include significant fluctuations in the measured temperature as well as large throughput changes, owning to the on-board application. Our investigation includes an analysis of a simple feedback configuration as well as feed-forward control structure. It is concluded that the feedback only method is insufficient for the unique challenges associated with on-board operation, which include fast start-up and quick load changes. While the feed-forward configuration improves performance, we found a fair amount of sensitivity with respect to model mismatch. The general conclusion is that some form of advanced control will be needed to meet the stringent performance requirements of the on-board fuel processor application.     

Noise spectrum and signal transmission through a population of spiking neurons.

How reliably can a population of spiking neurons transmit a continuous-time signal? We study the noise spectrum of a fully connected population of spiking neurons with relative and absolute refractoriness. Spikes are generated stochastically with a rate that depends on the postsynaptic potential. The analytical solution of the noise spectrum of the population activity is compared with simulations. We find that strong inhibitory couplings can considerably reduce the noise level in a certain frequency band. This allows the population to reliably transmit signals at frequencies close to or even above the single-neuron firing rate.     

Linear space-time multiuser detection for multipath CDMA channels

We consider the problem of detecting synchronous code division multiple access (CDMA) signals in multipath channels that result in multiple access interference (MAI). It is well known that such challenging conditions may create severe near-far situations in which the standard techniques of combined power control and temporal single-user RAKE receivers provide poor performance. To address the shortcomings of the RAKE receiver, multiple antenna receivers combining space-time processing with multiuser detection have been proposed in the literature. Specifically, a space-time detector based on minimizing the mean-squared output between the data stream and the linear combiner output has shown great potential in achieving good near-far performance with much less complexity than the optimum space-time multiuser detector. Moreover, this space-time minimum mean-squared error (ST-MMSE) multiuser detector has the additional advantage of being well suited for adaptive implementation. We propose novel trained and blind adaptive algorithms based on stochastic gradient techniques, which are shown to approximate the ST-MMSE solution without requiring knowledge of the channel. We show that these linear space-time detectors can potentially provide significant capacity enhancements (up to one order of magnitude) over the conventional temporal single-user RAKE receiver     

The educational role of personal computers in power systemlaboratories

A set of power-system laboratory exercises performed on a microcomputer system is described. The interactive graphics environment is provided by a 16 bit microcomputer with 1 MB of main memory coupled to a color-graphics terminal. Three laboratory exercises are analytically described, involving economic generation scheduling, load flow studies, and fault calculations. The student reaction to the computerized laboratory exercises is commented on, and the potential problems are pointed out. The effect of these exercises in developing the engineering intuition and integrating the power-system analysis education of the electrical engineering student is outlined     

Analysis of trace impurities in hydrogen: Enrichment of impurities using a H2 selective permeation membrane

A laboratory-scale gas sampling and impurity enrichment device (GSIED) using a Pd/Cu-coated Pd–Ag alloy hydrogen selective permeation membrane has been designed, fabricated, and tested to show that such a device provides an effective method to enrich trace impurity species in hydrogen by factors of 10–100 or greater. The enrichment process will allow analysis of these impurities in hydrogen using simpler and less expensive analytical instruments that can be deployed in the fields. A series of experiments was conducted with the device using a hydrogen analyte gas containing N₂, CH₄, and CO₂ at ∼0.1% each, CO at ∼100 ppm, and H₂S at ∼2 ppm. Chemical analyses of the impurity-enriched sample showed that for the non-sulfur species, the measured enrichment factors were 14.5–14.9, which closely matched the calculated enrichment factors of 14.8–14.9. The elemental material balances indicated a good accounting of the non-sulfur impurity species. For the sulfur species, some initial sulfur loss was observed, presumably due to interaction with the surfaces and/or analytical deficiencies. The impurity enrichment factors for such sampling devices are functions of the sampler size, and the sample vessel pressures before and after enrichment. Depending on the volume of the enriched sample needed for analysis, the device can be designed to enrich the impurities in hydrogen by more than a factor of two orders of magnitude for practical and economical field applications.     

Preparation and characterization of adipic acid-modified starch microparticles/plasticized starch composite films reinforced by lignin

In this article, starch microparticles (SM) were prepared by delivering ethanol as the precipitant into starch paste solution dropwise. Adipic acid (AA)-modified starch microparticles (AASM) were fabricated using the dry preparation technique. The composites were prepared using AASM as the filler in glycerol plasticized-corn starch (GCS) matrix by the casting process. Two lignins were also compared in terms of structure and reactivity when incorporated within the AASM–GCS matrix. The effects of lignin on the morphology, surface properties, and water sorption, as well as mechanical and thermal properties of starch–lignin composite films were investigated. The surface water resistance and the thermal stability of materials were improved through addition of lignin. Starch–lignin composite materials presented higher tensile strength, but a lower elongation capacity comparatively with those without lignin.