Cross‐Coupled Ratio Control Structure

Abstract

In this paper, a cross‐coupled ratio control structure with two blend stations has been proposed. The main feature of the proposed structure is to give a good ratio performance for both set‐point changes and load disturbances that might occur in any one of the two loops. A simple tuning procedure for the inner controllers of the two loops and an easy design methodology for the blend stations have been proposed in order to avoid any significant tuning and design effort for the implementer. The proposed structure is realized on a microcontroller based system. This cross‐coupled ratio control structure that has been embedded into the microcontroller is then used to maintain the prescribed ratio “a” of the two processes, namely heat transfer process trainer (PT 326‐Feedback) and process control simulator (PCS 327‐Feedback). The same two processes are run under another alternative ratio control structure and the results are compared with each other.     

Predicting the unconfined compressive strength of the Breathitt shale using slake durability, Shore hardness and rock structural properties

Compressive strength is the most widely used design parameter in the construction industry and in rock engineering. For example, Bieniawski [Bieniawski, Z. T., Estimating the strength of rock materials, Is. J. S. Afr. Inst. Min. Metall., 1974, 74, 312–320.] reported that mining engineers request the uniaxial compressive strength (UCS) more often than any other rock property. However, standards set for specimen preparation are very demanding. Therefore it is quite difficult and sometimes impossible to fulfill these requirements using weak rocks and especially shales. This paper evaluates the use of the slake durability and Shore hardness tests to estimate UCS, based on laboratory correlations performed for this study and others and based on analysis of structural and physical material properties affecting both strength and durability.     

Improvements in Noise Suppression for I/O Circuits Using Embedded Planar Capacitors

The performance of embedded planar capacitors in noise suppression of input/output (I/O) circuits and improvements in board impedance profile have been investigated in this paper. Simultaneous switching noise (SSN) is a critical issue in today's systems and this paper shows performance improvements by introducing thin planar embedded capacitors in the board stack up. Measurement and modeling results by including the effects of transmission lines and the power ground plane pairs in the board stack up in the gigahertz range quantify the performance of the embedded capacitors.     

Defects in nickel ferrite thin films grown by chemical vapour deposition

Thin single-crystal films of nickel ferrite have been grown on magnesia substrates. The structure of the films has been examined using X-ray diffraction, scanning electron microscopy and transmission electron microscopy and diffraction. The films are characterized by arrays of planar faults on {110} due to faults in cation arrangements in the nickel ferrite spinel lattice. The origin of these defects is discussed.     

Mechanics and dynamics of general milling cutters.: Part I: helical end mills

A variety of helical end mill geometry is used in the industry. Helical cylindrical, helical ball, taper helical ball, bull nosed and special purpose end mills are widely used in aerospace, automotive and die machining industry. While the geometry of each cutter may be different, the mechanics and dynamics of the milling process at each cutting edge point are common. This paper presents a generalized mathematical model of most helical end mills used in the industry. The end mill geometry is modeled by helical flutes wrapped around a parametric envelope. The coordinates of a cutting edge point along the parametric helical flute are mathematically expressed. The chip thickness at each cutting point is evaluated by using the true kinematics of milling including the structural vibrations of both cutter and workpiece. By integrating the process along each cutting edge, which is in contact with the workpiece, the cutting forces, vibrations, dimensional surface finish and chatter stability lobes for an arbitrary end mill can be predicted. The predicted and measured cutting forces, surface roughness and stability lobes for ball, helical tapered ball, and bull nosed end mills are provided to illustrate the viability of the proposed generalized end mill analysis.     

Buffer effects on the mosaic structure of the HR-GaN grown on 6H-SiC substrate by MOCVD

High-resistive GaN (>10⁸ Ω cm) layers have been grown with different buffer structures on 6H-SiC substrate using metalorganic chemical vapor deposition reactor. Different combination of the GaN/AlN super lattice, low temperature AlN, high temperature AlN and Al_xGa_1?xN (x ≈ 0.67) layers were used in the buffer structures. The growth parameters of the buffer layers were optimized for obtaining a high-resistive GaN epilayer. The mosaic structure parameters, such as lateral and vertical coherence lengths, tilt and twist angle (and heterogeneous strain), and dislocation densities (edge and screw dislocations) of the high-resistive GaN epilayers have been investigated using x-ray diffraction measurements. In addition, the residual stress behaviors in the high-resistive GaN epilayers were determined using both x-ray diffraction and Raman measurements. It was found that the buffer structures between the HR-GaN and SiC substrate have been found to have significant effect on the surface morphology and the mosaic structures parameters. On the other hand, both XRD and Raman results confirmed that there is low residual stress in the high-resistive GaN epilayers grown on different buffer structures.     

Evaluation of Natural Gas Supply Security in Turkey with Future Projection

Natural gas is one of the key energy resources for Turkey due to fact that 32% of annual primary energy supply and 45% of annual electricity production is obtained from natural gas with also common usage of residential and industrial zones. In this study, the supply security of natural gas was taken into consideration with strategic criteria of energy policy with the SWOT （strengths, weaknesses, opportunities and threats） analysis and the future projection for Turkey. It has been concluded on geopolitics criteria, domestic production and research for resources must be stimulated as high as possible and participation to abroad resources must be implemented.