Robust Stability of Networked Load Frequency Control Systems with Time-Varying Delays

In deregulated power system scenario coupled with smart grid technology, for networked load frequency control (LFC), an open communication structure, owing to low cost and flexibility, is preferred over dedicated networks in the feedback control loop for transmitting/receiving the data between the geographically displaced power system and the control center. In such a control scheme, closing the feedback loop through an open communication channel, in turn, introduces two additive time-varying delays of dissimilar characteristics in the feedback path. These delays degrade the performance of the closed-loop system, and exert a destabilizing effect on the overall system. In this paper, using Lyapunov-Krasovskii functional approach, a less conservative stability criterion is presented to ascertain delay-dependent stability of such network-controlled LFC systems with two additive time-varying delays in the feedback path in the presence of uncertain load disturbance conditions. Unlike the existing results, which are derived by combining these two delays into one, the proposed result considers the two delays as separate entities thereby imparting more generalization into the stability analysis. The effect of unknown exogenous load disturbance is incorporated by mathematically modeling them as a bounded non-linear time-varying function of current and delayed state vectors.     

A Generalized Relationship for Determination of Tensile Strength of Fine-Grained Soils from Shrinkage Characteristics

Tensile strength of fine-grained soils has been extensively investigated by earlier researchers and several methodologies have been evolved for its determination. However, either most of these methods are not valid/applicable for a wide range of moisture contents or they involve tedious sample/specimen preparation. In this context, the methodology of determining tensile strength by employing thin films, which is available in the literature, has been found to be quite handy and useful. It has been observed that a unique relationship exists among the tensile strength, moisture content, and shrinkage characteristics of fine-grained soils. This methodology is appreciable due to its applicability to a wide range of moisture contents, comparable ease of sample preparation and testing, and the obtained results lack generalization. Exhaustive tests were conducted on fine-grained soils of entirely different characteristics and generalized relationships have been proposed between the percentage linear shrinkage, tensile strength, and moisture content (defined as liquid to solid ratio). Based on a critical analysis of the results available in the literature, the efficiency of such relationships for determination of tensile strength of fine-grained soils has been demonstrated. In the authors’ opinion, such relationships would be quite useful for determining tensile strength of fine-grained soils from their linear shrinkage, which can easily be measured in a conventional geotechnical engineering laboratory.     

Harmonization of global third generation mobile systems

The International Telecommunication Union launched the third-generation project in 1986 with the aim to provide global personal communication using an inexpensive mobile terminal that can truly facilitate communication "anywhere, anytime". In previous years, standardization activities toward IMT-2000 have accelerated toward concrete specifications. By June 1998, a total of 15 proposals from around the world had been submitted to the ITU as radio transmission technology candidates. Since then, the 3G standardization landscape has seen many changes-a steady progression of the convergence process. This article provides a comprehensive overview of the worldwide harmonization efforts on the standardization of third-generation terrestrial mobile communication systems. The status, as of October 1999 when this article was written, of the technical specifications within 3G partnership projects are also summarized.     

Dielectric properties of 3d transition metal substituted BaTiO3 ceramics containing the hexagonal phase formation

The role of transition metals of the 3d series from V (Z = 23) to Zn (Z = 30) is investigated in modifying the crystallographic phase contents, microstructure and the dielectric properties of BaTiO₃ ceramics containing ≤10 at% substituents. All the transition metals brought about the phase conversion to hexagonal BaTiO₃ and the hexagonality is found to depend on Ba/Ti ratio as well as the processing conditions including the sintering temperature and the post sinter annealing. The ε_r-T characteristics are modified with increasing hexagonality by way of the tremendous decrease in dielectric constant with broad and diminished ε_max for the mixed phase ceramics giving way to flat ε_r-T curves for totally hexagonal specimens. Doping with >1% Zn²⁺ or ≥5% Mg²⁺ also render the ceramics completely hexagonal indicating that the crystal field effects of the 3d orbital electrons are not the cause for the conversion to hexagonal phase. Electron paramagnetic resonance (EPR) spectra of Mn-doped ceramics reveal the prevalence of defect complexes involving oxygen vacancies and different valence states of Mn occupying the Ti-sites within the corner-sharing as well as face-sharing octahedra present in hexagonal BaTiO₃. EPR results also indicate defect complexes involving electron localization at Ti-sites and oxygen vacancies around the face-sharing octahedra. On annealing the ceramics in lower oxygen partial pressures at elevated temperatures leads to the reversion to corner shared (Ti³⁺–V_O) defect complex accompanied by the conversion to cubic/tetragonal phase. The alterations in the oxygen vacancy-metal impurity defect complexes and the modifications in the oxygen close packing are the cause for the prevalence of hexagonal BaTiO₃ at room temperature.     

Odour Cues from Fruit Arils of Artocarpus heterophyllus Attract both Sexes of Oriental Fruit Flies

Journal of Chemical Ecology - The Oriental fruit fly, Bactrocera dorsalis (Hendel) is an economically devastating pest of fruit crops across the globe with stringent quarantine restrictions to...     

Making use of prognostics health management information for aerospace spare components logistics network optimisation

Although research has evolved significantly over the last decade, there are still a large number of Grand Challenges confronting modelling, model deployment, and model-based decision making of large-scale complex Discrete Event Logistics Systems (DELS) to be tackled, as identified and reviewed during a Dagstuhl workshop in March 2010. This paper illustrates how several of these challenges are already being addressed, based on a series of case studies from the Aerospace Spare Components Logistics domain, where consolidated operational Prognostics and Health Management (PHM) information can be used for tactical planning and optimisation of spare components logistics networks. In this setting, the growing potential of PHM technology to facilitate the maintenance and support of commercial and military aircraft emphasises the need for tools to determine the impacts and benefits of a PHM system. To achieve this, the prognostics parameters and related logistics policies were identified, modelled, and subsequently incorporated into a simulation-based decision support framework.     

Error rates for Nakagami-m fading multichannel reception of binaryand M-ary signals

This paper derives new closed-form formulas for the error probabilities of single and multichannel communications in Rayleigh and Nakagami-m (1960) fading. Closed-form solutions to three generic trigonometric integrals are presented as part of the main result, providing a unified method for the derivation of exact closed-form average symbol-error probability expressions for binary and M-ary signals with L independent channel diversity reception. Both selection-diversity and maximal-ratio combining (MRC) techniques are considered. The results are generally applicable for arbitrary two-dimensional signal constellations that have polygonal decision regions operating in a slow Nakagami-m fading environments with positive integer fading severity index. MRC with generically correlated fading is also considered. The new expressions are applicable in many cases of practical interest. The closed-form expressions derived for a single channel reception case can be extended to provide an approximation for the error rates of binary and M-ary signals that employ an equal-gain combining diversity receiver     

IGNITION DELAY OF DROPLET CLOUDS: RESULTS FROM GROUP COMBUSTION THEORY

The ignition and evaporation of spherical cloud of droplets in a hot quiescent atmosphere is examined numerically using transient group combustion analysis. Ignition delay times are calculated as a function of cloud radius, ambient temperature, drop size and droplet number density. The ignition temperature for a cloud of drops was found to be less than that obtained from a single drop. The results indicated an interaction between chemical and physical effects resulting in the possibility of an optimal interdrop spacing for ignition of a fuel with a high boiling point. The model results indicate that for interdrop spacing to radius ratio of less than 5, the ignition and evaporation of a cloud of drops is confined to a thin layer at the surface of the cloud. For drops spaced farther apart thermal penetration from the hot ambient is possible resulting in vaporization within the cloud.     

Analyzing multi-hop routing feasibility for sensor data harvesting using mobile sinks

This paper presents a modeling framework for characterizing the feasibility and impacts of multi-hop packet routing in sensor networks with mobile sinks. Data collection in sensor networks using mobile sinks has recently been investigated to improve energy performance at the cost of collection delay. Although the data collection can be accomplished with varying degrees of multi-hop routing, for a given data generation rate, as the extent of multi-hop routing increases, the round traversal time of the sink decreases. At the same time, the interference experienced by the mobile sink-to-sensor links and the consequent upload time go up. This paper characterizes these competing effects and develops a methodology for determining the extent of multi-hop routing that is feasible for given network and application parameters such as sensor data generation rate, wireless link capacity between sensors and mobile sink, the speed of the mobile sink and node density.