HIERARCHICAL AND MODULAR MODELING OF STRUCTURAL STEEL ERECTION PROCESS USING PETRI NETS

The construction industry is growing at a fast pace-newer project delivery methodo logies are being adopted; design of facilities is continuously improving, newer means, methods, and materials of construction are being used. All these market forces have re sulted in an increase in complexity of on-site construction processes. The construction industry needs advanced tools and techniques to plan and manage these complex con struction processes. This paper describes and utilizes a Petri Net based hierarchical and modular modeling and analysis technique for the planning of complex construction pro cesses. Petri Nets are graphical modeling tools that have been utilized in the modeling and analysis of processes in the fields of software engineering, telecommunications, manufac turing, and construction. This paper highlights advanced features of Petri Nets and their utilization in the modeling and analysis of structural steel erection processes. Through the use of hierarchy, modularity, and resource modeling Petri Nets provide clear advan tages in the modeling of complex construction processes.     

AI-based adaptive control and design of autopilot system for nonlinear UAV

The objective of this paper is to design an autopilot system for unmanned aerial vehicle (UAV) to control the speed and altitude using electronic throttle control system (ETCS) and elevator, respectively. A DC servo motor is used for designing of ETCS to control the throttle position for appropriate amount of air mass flow. Artificial Intelligence (AI)-based controllers such as fuzzy logic PD, fuzzy logic PD + I, self-tuning fuzzy logic PID (STF-PID) controller and fuzzy logic-based sliding mode adaptive controller (FLSMAC) are designed for stable autopilot system and are compared with conventional PI controller. The target of throttle, speed and altitude controls are to achieve a wide range of air speed, improved energy efficiency and fuel economy with reduced pollutant emission. The energy efficiency using specific energy rate per velocity of UAV is also presented in this paper.     

Polarization and Conduction Mechanism in Mixed-Alkali Glasses

Thermally stimulated polarization and depolarization current (TSPC/TSDC) measurements on mixed alkali (Li-Na) silicate glasses show two TSDC peaks along with a dc conduction current at high temperatures, similar to single-alkali silicate glasses. The activation energies for the two TSDC peaks and for dc conduction increase with the addition of a second alkali. The first TSDC peak does not change in size but the second becomes substantially smaller when the second alkali is added. The reduction in size of the second TSDC peak correlates well with the reduction in the dielectric loss hi mixed-alkali glasses. A model is proposed to account for the behavior of the two TSDC peaks.     

A review of designing machine tool for leanness

As an ideology, Leanness is not a new concept but still researchers strive for developing new methods to reduce almost all kinds of identified wastages at almost every stage and in every activity ?? right from design till delivery of final product to the end-customer. Newly developed manufacturing ideologies, paradigms and systems are always critically examined from the point of view of leanness. In other words, leanness is becoming an important evaluation tool to compare the recently developed/pioneered approaches. There has been a gradual evolution of the leanness over the years from the shop floor level of a manufacturing (automobile) organization to almost every operational and management aspect now. The Leanness has undergone and still is undergoing a process of continuous and never-ending evolution due to its inherently built dynamic concept of continuous improvement. Although in the literature a lot of work has been reported to the application of lean tools, principles, theories and methodologies to production systems, but a very few is evident in the area of Lean design process of a product and machine tool. For this reason an attempt is being made here to focus a significant proportion of this paper on evolutionary aspect of leanness from manufacturing to design stage. Also, this paper reviews the concepts and practices being followed till date by the industrialists, researchers and academicians in applying lean tools and techniques in the design of product and machine tools along with the methods to measure the lean improvements in the systems.     

Resistivity-Microstructure Relations in Lithia-Stabilized Polycrystalline β"-Alumina

The sodium ion resistivity of lithia-stabilized polycrystalline β"-alumina was measured as a function of temperature for fine-grained and coarse-grained specimens with a chemical composition of 8.80 Na₂0-0.75 Li₂O-90.45 A1₂O₃ (wt%). A model is presented which explains the dependence of sodium ion resistivity on grain size. Using the model the activation energy was determined for the transport of sodium ions across a grain boundary in this form of sodium β"-alumina.     

High-Temperature Density Determination of Boron Oxide and Binary Rubidium and Cesium Borates

Density determinations of pure B₂O₃ and binary rubidium and cesium borates have been made in the temperature ranges 450° to 1300°C and 500° to 1100°C respectively. The density of B₂O₃ can be represented between 600° and 1000°C as d = 1.3388 + 228 (1/T) and for temperatures above 1000°C as d = 1.3947 + 157.9 (1/T), where d is in grams per milliliter and T is in °K. The volume expansion (dV/dT) in the alkali borate systems at 800°C increases with an increase of alkali oxide when the alkali concentration is more than 18 mole %. This increase in the volume expansion follows the order Cs > Rb > K > Na > Li. In the range 15 to 20 mole % alkali oxide a break in the volume expansion was observed. This break suggests a possible change in the structural configuration of the alkali borates.     

Kinetics of Spinodal Decomposition in the TiO2-SnO2 System: The Effect of Aliovalent Dopants

Dense samples in the TiO₂-SnO₂ system were fabricated by pressureless sintering in air using commercial powders as well as powders obtained by coprecipitation. Phase equilibria in the system were examined using X-ray diffraction on samples that were annealed for long periods of time. Samples of near equi-molar composition made with controlled amounts of Al and Ta (separately) as dopants were annealed inside the coherent spinodal. X-ray diffraction and electron microscopy were the principal characterization tools used to follow the kinetics of phase transformation. The composition modulations occurred along the [001] direction consistent with prior work. During the early stages of the decomposition process, interlamellar surfaces were coherent. At later stages, strain mismatch was accommodated by interface dislocations. The kinetics of decomposition were strongly influenced by the type and the amount of dopant. Specifically, trivalent aluminum enhanced the decomposition while pentavalent tantalum suppressed it. The kinetics in a sample doped with 0.5 mol% Al₂O₃ were more than 3 orders of magnitude more rapid than a sample doped with 1.0 mol% Ta₂O₅. These observations are rationalized on the premise that cation interstitial mobility is greater than cation vacancy mobility.     

Viscosity Determination of Boron Oxide and Binary Borates

The anomalous behavior of rubidium and cesium borate glass and the boron coordination in alkali borate liquids are discussed. The viscosity-composition isotherms of rubidium and cesium borates have been found to follow the same trend as those of other alkali borates. For boron oxide at temperatures between 500° and 775°C, the activation energy for viscous flow, E_vis= (4.213 × 10⁴) (1/T) - 22.15 and for temperatures above 775°C, E_vis= (1.121 × 10⁴) (1/T) + 7.40, in which T is in °K. The activation energies for viscous flow, E_vis, in kcal per mole, increase with all molten alkali borates in the order Li > Na > K > Rb > Cs to about 20 mole % of akali oxide. This phenomenon is explained on the basis of Douglas's hole theory.