Neural networks and fuzzy logic-based spark advance control of SI engines

In SI engines, spark advance (SA) needs to be controlled to get Maximum Brake Torque (MBT) timing. Spark advance can be controlled either by open loop or by closed loop controller. The open loop controller requires extensive testing and calibration of engine, to develop look up tables. In closed loop controller, empirical rules relating variables deduced from cylinder pressure are used. One of such empirical rules is to fix location of peak pressure (LPP) at a desired value of the crank angle. In the present work, a combined neural network and fuzzy logic-based control scheme is designed for SA control to get MBT timing. The fuzzy logic controller is designed to maintain LPP of SI engine close to 16° ATDC. The controller works in conjunction with Recurrent Neural Network model for cylinder pressure identification. LPP is estimated from cylinder pressure curve reconstructed using neural network model and is used as feedback signal to fuzzy logic controller. The simulations have been carried out to test the performance of the combined neural network and fuzzy logic-based control strategy. The simulation results show that the proposed strategy can quite satisfactorily control LPP to its desired value.     

Terminal slider control of robot systems

Many robotic systems would, in the future, be required to operate in environments that are highly unstructured (with varying dynamical properties) and active (possessing means of self-actuation). Although a significant volume of results exist in model-based, robust and adaptive control literature, many issues pertinent to the stabilization of contact interactions with unpredictable environments remain unresolved, especially in dealing with large magnitude and high frequency parametric uncertainties. The primary intent of this paper is nonlinear control synthesis for robotic operations in unstructured environments. We introduce the notion oftime constrained terminal convergence for controlled systems, and propose an approach to nonlinear control synthesis based upon a new class of sliding modes, denotedterminal sliders. Terminal controllers that enforce finite convergence to equilibrium are synthesized for an example nonlinear system (with and without parametric uncertainties). Improved performance is demonstrated through the elimination of high frequency control switching, employed previously for robustness to parametric uncertainties [2]. The dependence of terminal slider stability upon the rate of change of uncertainties over the sliding surface, rather than the magnitude of the uncertainty itself, results in improved control robustness. Improved reliability is demonstrated through the elimination ofinterpolation regions [2]. Finally, improved (guaranteed) precision is argued for through an analysis of steady state behavior.A preliminary version of this paper appeared as a JPL Engineering Memorandum # 347-90-284, Jet Propulsion Laboratory, Pasadena, CA, December 1990.     

A NEW VIEW OF INFORMATION MODELING

The information model was conceived to address the complexities of managing large volumes of data, processes, designs, and tools that are shared by many business users with differing requirements. Because an information model derives much of its features from data models, the distinction between information modeling and data modeling is sometimes unclear. One perspective is that information modeling is context dependent: when a model is viewed as a representation scheme for users to comprehend, it is an information model. When used as a representation scheme to be processed by a computer, it is a data model.     

Changes in the glaciers of Chandra–Bhaga basin,Himachal Himalaya,India, between 1980 and 2010 measured using remote sensing

This study reports the glacier changes of Chandra–Bhaga basin, northwest Himalaya, India, from 1980 to 2010. Satellite remote-sensing data from the Landsat Multispectral Scanner (MSS) and Thematic Mapper (TM), the Linear Imaging Self Scanning Sensor (LISS) and Advanced Wide Field Sensor (AWiFS) of the Indian Remote Sensing (IRS) series, and the Shuttle Radar Topography Mission (SRTM) digital elevation model (DEM) were used to study the changes in glacier parameters such as glacier area, length, snout elevation, and the impact of glacier topographical parameters (glacier slope, aspect, and altitude range) on the glacier changes. It was found that the total glaciated area had shrunk to 368.2 km² in 2010 from 377.6 km² in 1980, a loss of 2.5%. The average position of glacier terminuses retreated by 465.5 ± 169.1 m from 1980 to 2010 with an average rate of 15.5 ± 5.6 m year^?1. The decadal scale analysis showed that the average rate of retreat had increased the most in the recent decade. A moraine-dammed lake located in the study region was found to have expanded in area from (0.65 ± 0.01) km² in 1980 to (1.26 ± 0.03) km² in 2010. Glaciers with steep slope and less altitude range have lost more area than the glaciers having gentle slope and greater altitude range.     

Dwell-Fatigue of Ni-Based Superalloys with Serrated and Planar Grain Boundary Morphologies: The Role of the γ′ Phase on Strain Accumulation and Cavitation

The effect of grain boundary (GB) morphology on the cavitation behavior in a Ni-based superalloy, RR1000, was studied during elevated temperature dwell-fatigue at 700 °C. Following a solution heat treatment, the material was control cooled at two different rates, resulting in high angle GB morphologies that were tailored as either serrated or planar. The resulting γ′ precipitate structures were characterized near GBs and within grains. Along serrated GBs coarsened and elongated γ′ precipitates formed and consequently created adjacent regions that were denuded of γ′ precipitates. Cyclic dwell-fatigue experiments were performed at low and high stress amplitudes to vary the amount of imparted strain on the specimens. A combination of electron backscatter diffraction and digital image correlation were used to resolve strain localization relative to the GBs, in which strain accumulation was found to precede cavity formation. Additionally, the regions denuded of the γ′ precipitates were observed to localize strain and to be initial sites of cavitation. These results present a quantitative strain analysis between two variants of an RR1000 alloy, which provides the micromechanical rationale to assess the increased proclivity for serrated GBs to form cavities.

     

Microstructure and microhardness in alumina gel monoliths

Alumina gel monoliths prepared from aluminium isopropoxide through hydrolysis and chemical polymerization are porous, transparent, and consist of ultrafine particles. The monolithic xerogels exhibit lamellar, cellular and fractal microstructures which are found to arise due to instabilities during drying. Phase separation can occur during ageing and drying and influence the microstructure. The Vickers indentation hardness shows a power-law dependence on relative density.     

Structural, Dielectric, Pyroelectric and Ferroelectric Properties of Glass Nano Composite: Lithium Borate-Strontium Bismuth Vanadium Niobate

Transparent glasses in the system (100 - x) (Li₂O - 2B₂O₃) - x (SrO - Bi₂O₃ - 0.7 Nb₂O₅ - 0.3 V₂O₅) (10 ≤ x ≤ 60, in molar ratio) were fabricated via the melt quenching technique. The as-quenched samples were X-ray amorphous. Differential thermal analysis (DTA) confirmed the glassy nature of the as-quenched samples. Strontium bismuth vanadium niobate nanorods were grown by controlled heat-treatment of the as-quenched glasses at 783 K for 6 h. The formation of nanorod layered perovskite SrBi₂(Nb_0.7V_0.3)₂O_9-δ (SBVN) phase via an intermediate fluorite phase was confirmed by both X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). The dielectric constants of both the as-quenched and heat-treated samples (783 K/6 h) increased while the dielectric loss (D) decreased with increasing x (SBVN content). Interestingly, the dielectric constant of the glass nanocrystal composite (heat-treated at 783 K/6 h) exhibited an anomaly in the vicinity of the crystallization temperature of the host glass (Li₂B₄O₇) reaching a value as high as ≈10⁶ at 800 K. These glass nanocrystal composites were pyroelectric and ferroelectric at 300 K.

Communicated by George W. Taylor