Manufacturing planning and control: The evolution of MRP and JIT integration

Material Requirements Planning (MRP) and Just-in-Time (JIT) system are directed toward planning and controlling the important characteristics of material flow: how much of what materials flow and when. Since the material flow is at the heart of the manufacturing firm, MRP and JHT are the powerful management tools that could determine the success or failure of an entire manufacturing system. One of the strongest debates in manufacturing has been centered on the performance comparison and compatibility of JIT production system to the existing MRP. The primary intent of this research is to provide an overview of the manufacturing planning and control environment associated with MRP and JIT. Classifying the existing MRP/JIT comparison and integration literature, two different perspectives on MRP/JIT are discussed, and future research area is proposed based on the taxonomy.     

Change of Color Appearance in Photopic,Mesopic and Scotopic Vision

Mesopic vision describes a range of light levels where vision is mediated by both cones and rods. The appearance of color in mesopic vision differs drastically from that in photopic vision, where only cones mediate visual information. We used a haploscopic color matching technique to investigate the color appearance under various illuminance levels, ranging from photopic to scotopic via mesopic levels. The observers did color matching between a test color chip under various illuminance levels and a matching color stimulus presented on the Cathode-Ray Tube (CRT) display under the photopic illuminance condition. The results showed that not only chroma and lightness but hue of most color chips changed with illuminance. The manner of the hue changed depended on the color of the test chip, while matching points approached a neutral gray with decrease in illuminance level for all test chips. Chroma reduced continuously with decrease of the illuminance level until 0.1 lx for reddish and yellowish color chips or until 1 lx for greenish and bluish ones. Beyond those illuminance levels, chroma was approximately constant. Lightness decreased with decreasing illuminance level for all test chips except bluish color chips, for which lightness did not decrease much in general and even increased in some cases as predicted by the Purkinje shift. The experimental results obtained in the present study provide critical features that should be considered in predicting the appearance of color at low light levels.     

Auger spectroscopy and properties of Ir(Pt)/PZT(PZT/PT)/Ir nanosized thin-film structures

Studies of the elemental distribution profiles through the thickness of thin-film ferroelectric capacitor structures using Auger spectroscopy made it possible to establish the relation between the elemental and phase composition of the structures, on the one hand, and their electrophysical properties, on the other. Special features were observed in the behavior of the lead titanate underlayer both in the as-fabricated and aged structures. It is shown that the variation in the characteristics of the capacitor structures during aging is caused by diffusion of the elements at the interfaces and in the PZT film against a background of a significant increase in the oxygen concentration. As a result, interface-modifying oxide layers form and the trap density on the upper and lower interfaces decreases in all samples.     

Effects of anodizing conditions on bond strength of anodically oxidized film to titanium substrate

The bond strength of the oxide film to the titanium substrate and its inherent structural characteristics are very important preconditions for the success of titanium implants. The purpose of this study was to evaluate the micro-morphologies, crystalline structures, and bond strengths of the anodically oxidized films formed on titanium with the variation of electrolytes and applied current densities. In contrast to the specimens produced using sulfuric acid as the electrolyte, those produced using phosphoric acid showed quite different shapes and densities of the pores as the applied current densities were varied. The oxide films anodized in sulfuric acid consisted of anatase and rutile TiO₂, whileTiP₂O₇ was predominantly formed on the Ti surfaces anodized using phosphoric acid as the electrolyte. The oxide films, which did not experience spark deposition showed amorphous shape and their bond strengths were significantly lower than those of the other groups (p < 0.05). Those specimens which experienced initial spark deposition with a low current condition showed the highest bond strengths (34.2 MPa) within each electrolyte sub-set. The growing rates of the oxide film thicknesses in relation to the electric current changes varied according to the type of electrolyte, and the oxide film thickness influenced the bond strength.     

Imaging characterization of carbon nanotube tips modified using a focused ion beam

A carbon nanotube (CNT) tip, which assembled on the sharp end of a Si tip by dielectrophoresis, was structurally modified using focused ion beam (FIB). We described the imaging characterization of the FIB-modified CNT tip in noncontact AFM mode in terms of wear, deep trench accessibility, and imaging resolution. Compared to a conventional Si tip, the FIB-modified CNT tip was superior, especially for prolonged scanning over 10 h. We conclude that modified CNT tips have the potential to obtain high-quality images of nanoscale structures.     

C-band continuously tunable lasers using tunable fiber Bragg gratings

We report the development of a ring tunable fiber laser based on tunable fiber Bragg gratings (TFBG) integrated with an optical circulator. The TFBG is embedded inside a 3-piont bending device for wavelength tuning. The tunable laser operating in the C-band has power variation, tuning resolution, tuning range and laser line width of ±0.5 dB, 0.5 nm, 25.0 nm and less than 0.05 nm, respectively. As 40 mW of pump power is used, the ring tunable laser has a side mode suppression ratio of 60 dB and a power conversion efficiency of 25%. These specifications ensure the high-quality operation of a tunable laser.     

Frequency stabilization of multiple semiconductor lasers using digital feedback loop

We propose and demonstrate a simple technique to stabilize the frequencies of multiple semiconductor lasers simultaneously using a Fabry-Perot etalon filter and a digital signal processing. Unlike other stabilization techniques, the proposed technique could stabilize DFB lasers using only one digital feedback control loop. The result shows that the proposed technique could maintain the frequency stability of 16 DFB lasers within ±150 MHz.     

Holographic angle multiplexing combined with peristrophic multiplexing in a photorefractive LiNbO3 crystal

We have investigated angle multiplexing combined with peristrophic (rotational) multiplexing in a photorefractive LiNbO₃ crystal of cylindrical shape. The peristrophic multiplexing was achieved by rotating the recording medium while the angle multiplexing, by varying the incident angle of the reference beam. Angle multiplexing in synchronization with rotation of the sample made it possible to continuously record and retrieve holograms. In the combined multiplexing, holograms were stored at different peristrophic positions and thus their angular selectivity could be much improved in comparison to that of only angle-multiplexed holograms. The theoretical angular selectivity was derived, along with its dependence on the sample rotation. The experimentally measured selectivity was in agreement with the theoretical one. The angular selectivity of angle-multiplexed holograms was measured to be 0.03° in the absence of sample rotation and it became less than 0.0075° with a sample rotation by 5.4°.     

Myocardial injury occurs earlier than myocardial inflammation in acute experimental viral myocarditis

Endomyocardial biopsy often fails to show myocardial inflammation for patients with clinically suspected myocarditis. The serum isoforms of troponin T (cTnT) level is a very sensitive marker of myocardial injury and it is elevated even in the absence of myocardial inflammation. We investigated the correlations for myocardial injury, virus titers and inflammation in acute viral infection. Using the murine coxsackievirus group B3 (CVB3) myocarditis model, the histopathologic findings and virus titers in mouse hearts were compared with the serum cTnT levels measured by ELISA at various time points. Viable virus titers in the hearts peaked at 3 days after infection (8.22 +/- 0.13 log10 PFU/100 mg of heart); they decreased at day 7 and no viable virus was detected from day 14. Myocardial inflammation was minimal at day 3, peaked at day 7 and markedly decreased at day 14. The individual serum TnT levels were significantly increased at day 3 (7.37 +/- 1.46 ng/ml), persisted to day 7 (0.73 +/- 0.08 ng/ml), and normalized at day 14. Serum cTnT levels were correlatable with virus titers in the heart (r = 0.744, P <0.01), but the serum cTnT levels were not correlated with the degrees of inflammation. Using the less myocarditic strain of CVB3, similar relationships were observed between the changes for the serum cTnT levels and the heart virus titers. During the course of viral infection, myocardial injury precedes the pathologic evidence of inflammation, and the elevated cTnT levels provide evidence of myocardial injury even in the absence of any histologic findings of myocarditis.