Development of censored data-based robust design for pharmaceutical quality by design

Robust design techniques, which are based on the concept of building quality into products or processes, are increasingly popular in many manufacturing industries. In this paper, we propose a new robust design model in the context of pharmaceutical production research and development. Traditional robust design principles have often been applied to situations in which the quality characteristics of interest are typically time insensitive. In pharmaceutical manufacturing processes, time-oriented quality characteristics, such as the degradation of a drug, are often of interest. As a result, current robust design models for quality improvement which have been studied in the literature may not be effective in finding robust design solutions. To address such practical needs, this paper develops a robust design model using censored data, which is perhaps the first attempt in the robust design field. We then study estimation methods, such as the expectation–maximization algorithm and the maximum likelihood method, in the robust design context. Finally, comparative studies are discussed for model verification via a numerical example.     

Corrosion and inhibition process of carbon steel in LiBr-H2O solution

Journal of Mechanical Science and Technology - Lithium bromide (LiBr)-H2O triple-effect absorption chillers are supposed to have a much higher carbon steel corrosion rate under high temperature...     

Design of a slider-crank leg mechanism for mobile hopping robotic platforms

Legged locomotion has been widely researched due to its effectiveness in overcoming uneven terrains. Due to previous efforts there has been much progress in achieving dynamic gait stability and as the next step, mimicking the high speed and efficiency observed in animals has become a research interest. The main barrier in developing such a robotic platform is the limitation in the power efficiency of the actuator: the use of pneumatic actuators produce sufficient power but are heavy and big; electronic motors can be compact but are disadvantageous in producing sudden impact from stall which is required for high speed legged locomotion. As a new attempt in this paper we suggest a new leg design for a mobile robot which uses the slider-crank mechanism to convert the continuous motor rotation into piston motion which is used to impact the ground. We believe this new mechanism will have advantage over conventional leg mechanism designs using electronic motors since it uses the continuous motion of the motor instead of sudden rotation movements from stall state which is not ideal to draw out maximum working condition from an electronic motor. In order to control impact timing from the periodic motion of the piston a mechanical passive clutch trigger mechanism was developed. Dynamic analysis was performed to determine the optimal position for the mechanical switch position of the clutch trigger mechanism, and the results were verified through simulation and experiment. Development of a legged locomotion with two degrees of freedom, slider-crank mechanism for impact and additional actuation for swing motion, is proposed for future work.     

Numerical investigation of bolt fitting and fastening forces by elastoplastic finite element analysis

The bolt–flange fitting and detaching processes are numerically investigated by the updated Lagrangian elastoplastic finite element analysis. The elastoplastic behavior of the flange is modeled by the power-law plastic model with the isotropic strain hardening, while assuming the bolt to be rigid by virtue of the big difference in the material stiffness between bolt and flange. Through the parametric numerical analyses of the bolt–flange fitting and detaching processes with respect to the shape of the bolt cross-section, the characteristics of the bolt fitting and fastening forces are investigated. The validity of the simplified 2-D axisymmetric finite element model is examined through the comparison with the numerical results obtained by 3-D full finite element model. As well, the effects of the bolt petal number on these forces are investigated, and the experiment is performed to verify the numerical simulation.     

Qualitative verification of the dispersion level in nano-composite and its application to YD-128/MWCNT composite to assess the wear characteristics with respect to the dispersion level

We analyzed the wear characteristics according to dispersion level of MWCNT in YD-128/MWCNT composite. Specimens for this study were fabricated using mechanical stirrer after blending of YD-128 and MWCNT. To change the dispersion level, the mixture of YD-128/MWCNT was stirred using mechanical stirrer during different times, such as, 15, 30, 60, and 120 minutes. Because the direct measuring of dispersion level is difficult in the case of solid composite, we suggest an indirect method for checking qualitatively the dispersion level as follows. Firstly, using the AEH (asymptotic expansion homogenization) in-house code, we analyzed numerically the mechanical stiffness of composite using RVEs (representative volume elements) which are modeled with different dispersion level. According to the numerical results of RVEs, we verified that the mechanical stiffness is higher as the dispersion degree is better. Then, through the experimental tensile test of the fabricated specimens using UTM, we obtained that the mechanical stiffness is higher as the stirring time is longer. Consequently, we could ensure that the dispersion degree of the fabricated specimens is better as the mechanical stirring time is longer. Finally, we assessed the wear test using abrading machine with fabricated specimens. We confirmed that the abrasion loss is decreased according to the increasing of dispersion degree in the case of YD-128/MWCNT composites.     

Surface modification of rutile TiO2 by submerged arc discharge for improved photoreactivity

Titanium dioxide is well known for its photocatalytic activity, but it works effectively only in the ultraviolet (UV) range. Given the relatively low flux of solar UV that reaches earth, the potential of exploring its photocatalytic capacity for environmental protection applications is very limited. In this study, rutile, the least photocatalytic of the three existing titanium dioxide crystalline forms, was suspended in water or acetonitrile and treated with oxygen or argon plasmas, using a novel dense-medium plasma technology (submerged arc discharge). As a result of the plasma treatment, rutile particles were doped with various trace elements that originated in electrodes made of different metals. Subsequent analyses show that the photocatalytic capacity of plasma-modified rutile is comparable to or even better than that of unmodified anatase, the most photocatalytic form of titanium dioxides. The color change of TiO₂ samples after plasma treatment indicates that the modified rutile absorbs visible light and may therefore work as a photocatalyst in the visible range. Given the fact that rutile can be produced in large quantity more easily and cheaply than can anatase, these results are very encouraging and open up possibilities in using rutile for photocatalytic applications in the visible range. This paper was presented at the Third International Surface Engineering Congress and Exposition held August 2–4, 2004 in Orlando, FL.     

Simulations of the dielectric constant of bonding materials and field emission properties of CNT cathodes

The effect of the dielectric constant (k) of bonding materials in a screen-printed carbon nanotube (CNT) cathode on the field enhancement factor was investigated for high-efficiency CNT cathodes using the ANSYS software. The values obtained by a simulation study were compared to the experimental results obtained for screen-printed CNT cathodes. The field enhancement factor increased as the dielectric constant decreased, reaching a maximum value at a dielectric constant of 1, the value for a vacuum. The findings indicate that the larger sheet resistance of the bonding materials, after the firing process, can be attributed to the larger emission current of the CNT cathode. From these results, it was concluded that the best bonding materials for screen-printed CNT cathodes should have a low dielectric constant and a high sheet resistance. This finding can be used as criteria for selecting bonding materials for use in CNT pastes for highly efficient CNT cathodes.     

A two-photon fluorescent probe for lipid raft imaging: C-laurdan

The lipid-rafts hypothesis proposes that naturally occurring lipid aggregates exist in the plane of membrane that are involved in signal transduction, protein sorting, and membrane transport. To understand their roles in cell biology, a direct visualization of such domains in living cells is essential. For this purpose, 6-dodecanoyl-2-(dimethylamino)naphthalene (laurdan), a membrane probe that is sensitive to the polarity of the membrane, has often been used. We have synthesized and characterized 6-dodecanoyl-2-[N-methyl-N-(carboxymethyl)amino]naphthalene (C-laurdan), which has the advantages of greater sensitivity to the membrane polarity, a brighter two-photon fluorescence image, and reflecting the cell environment more accurately than laurdan. Lipid rafts can be visualized by two-photon microscopy by using C-laurdan as a probe. Our results show that the lipid rafts cover 38 % of the cell surface.     

The enhanced anodic performance of highly crimped and crystalline nanofibrillar carbon in lithium-ion batteries

To find a novel high-performance anode material for lithium-ion batteries, a new form of carbon characterized by highly crimped and crystalline nanofibrillar microtextures was produced by heat treating polyacrylonitrile/FeCl₃ hybrid precursor and subsequent thermal annealing under hydrogen gas. This form of carbon exhibits a rechargeable capacity of ∼630 mAh/g, which is superior to that of graphite, with a Coulomb efficiency of ∼70%. Further, the new form of carbon was found to exhibit an efficiency of lithium ion insertion/extraction of ∼100% in the voltage range from 0.06 to 0.80 V, with a capacity of ∼400 mAh/g. We speculate that this excellent capacity is due to the characteristic structure of this form of carbon, i.e. its highly entangled web-like hyperstructure consisting of highly crimped and crystalline nanofibrillar microtextures, which enables good permeation and has high resilience to volume deformation during the insertion/extraction of Li ions.