Dynamic modeling of a gas pressure control system for a gas‐assisted injection molding process

This study presents the development of dynamic models for gas injection pressure that may be implemented in the design of control systems for gas‐injection units. A nonlinear dynamic model was first derived and then verified by experimental measurements. This was done by using a laboratory‐built, gas‐assisted injection unit. The agreement between the prediction and measurement indicates that the present nonlinear dynamic model adequately predicts the dynamic behavior of gas injection pressure during the process. Although the resulting model is useful for understanding the behavior of the process and the effects of different process variables, its complexity may cause difficulties in a real control application. Therefore, a second‐order model based on the basic characteristics of the nonlinear model was proposed to approximate the gas injection pressure. In order to determine the model parameters, the algorithm of recursive least‐square system identification was employed. A comparison of simulated results of an identified model with experimental data showed that the model accurately predicted the transient behavior of gas injection pressure. Consequently, this low‐order model can be easily implemented into the control system design of a gas‐injection unit.     

Synthesis of Na0.5K0.5NbO3 Piezoelectrics by a Solution Coating Approach

The solution coating method is shown to provide more homogeneous mixing of the starting powders and purer (Na_0.5K_0.5)NbO₃ (NKN) powder than the conventional method thereby rendering cold isostatic pressing unnecessary. Sintering NKN with potassium copper niobate (KCN) by uniaxial pressing gave a relative bulk density of 92%, d ₃₃ coefficient of 112 pC/N and a loss factor of 1% after 6 h at 1100°C. In contrast, the conventional method yielded 84% relative bulk density and a 31% loss factor after 6 h at 1100°C and the sample was too porous to allow for dielectric and piezoelectric measurements.     

Scanning electron micrograph study of the impact-improved MBS/PVC blends

The improvement of the impact strength of the telecommunication equipment using injection moldable PVC/MBS and other modifiers were studied. The addition of MBS to the PVC was found with rapid increases in the impact stregths in Kg-cm/cm: 5.5 of pure PVC; 80 of 12 phr and the maximum of 131 of 20 phr of MBS. This increasing impact strength phenomena were subjected to close examinations of SEM, DMTA, and strain-stress diagrams. The DMTA analysis of the retaining of the individual T_g's of MBS and PVC in the MBS/PVC blends, indicates that no miscibility of MBS and PVC has occurred. The DMTA diagrams of 5, 12, 20, and 30 phrs of MBS in PVC were analyzed and the same samples were also subjected to the impact strength measurements and the SEM examinations. SEM photos showed a gradual transition of the linear to the three-dimensional arrangements had occurred in the PVC/MBS blends. The formation of three-dimensional arrangement occurred between 10–20 phr of added MBS. The spacial change from linear to the three-dimensional arrangements observed in SEM photos correlates the rapid increases of the impact strengths of the specimens tested. Injection specimens of the telephone sets made of PVC/MBS blends with 20 phr of MBS in PVC indicate that the impact strength is averaged at 115 Kg-cm/cm with tensile strength of 330 Kg/sq cm and elongation of 150%. The similar change of the spacial arrangement is also observed in their SEM photos.     

Highly Photoluminescent and Stable Aqueous ZnS Quantum Dots

We report an all-aqueous synthesis of highly photoluminescent and stable ZnS quantum dots (QDs) with water as the medium, i.e. first synthesizing ZnS QDs with 3-mercaptopropionic acid (MPA) as the capping molecule, followed by replacing some of MPA with (3-mercaptopropyl) trimethoxysilane (MPS). The resultant MPS-replaced ZnS QDs were about 5 nm in size with a cubic zinc blende crystalline structure, and had both MPA and MPS on the surface as confirmed by the Fourier Transform Infrared (FTIR) spectroscopy. They exhibited blue trap-state emissions around 415 nm and a quantum yield (QY) of 75% with Rhodamine 101 as the reference, and remained stable for more than 60 days under the ambient conditions. Through the capping molecule replacement procedure, the MPS-replaced ZnS QDs avoided the shortcomings of both the MPA-ZnS QDs and the MPS-ZnS QDs, and acquired the advantages of strong photoluminescence and good stability, which are important to the QDs' applications especially for bioimaging.     

A novel cross-coupling control design for Bi-axis motion

A new structure of cross-coupling controller for precise tracking in motion control is proposed in this paper. When compared with the conventional cross-coupling system, this new structure has the advantage that the compensators in CCC have a simpler design process than conventional ones and so does its stability analysis. The proposed compensator (or controller) is evaluated and compared experimentally with a traditional uncoupled controller on a microcomputer controlled dual-axis positioning system. The experimental results show that the new structure of cross-coupling controller remarkably reduces contour error. In addition, this new controller can be implemented easily on a majority of motion systems in use today via reprogramming the reference position command subroutine.     

Challenges in modern drug discovery: a case study of boceprevir, an HCV protease inhibitor for the treatment of hepatitis C virus infection

More than 170 million people worldwide are affected by the hepatitis C virus (HCV). The disease has been described as a "silent epidemic" and "a serious global health crisis". HCV infection is a leading cause of chronic liver disease such as cirrhosis, carcinoma, or liver failure. The current pegylated interferon and ribavirin combination therapy is effective in only 50% of patients. Its moderate efficacy and apparent side effects underscore the need for safer and more effective treatments. The nonstructural NS3 protease of the virus plays a vital role in the replication of the HCV virus. The development of small molecule inhibitors of NS3 protease as antiviral agents has been intensively pursued as a viable strategy to eradicate HCV infection. However, it is a daunting task. The protease has a shallow and solvent-exposed substrate binding region, and the inhibitor binding energy is mainly derived from weak lipophilic and electrostatic interactions. Moreover, lack of a robust in vitro cell culture system and the absence of a convenient small animal model have hampered the assessment of both in vitro and in vivo efficacy of any antiviral compounds. Despite the tremendous challenges, with access to a recently developed cell-based replicon system, major progress has been made toward a more effective small molecule HCV drug. In our HCV program, facing no leads from our screening effort, a structure-based drug design approach was carried out. An alpha-ketoamide-type electrofile was designed to trap the serine hydroxyl of the protease. Early ketoamide inhibitors mimicked the structures of the peptide substrates. With the aid of X-ray structures, we successfully truncated the undecapeptide lead that had a molecular weight of 1265 Da stepwise to a tripeptide with a molecular weight of 500 Da. In an attempt to depeptidize the inhibitors, various strategies such as hydrazine urea replacement of amide bonds and P2 to P4 and P1 to P3 macrocyclizations were examined. Further optimization of the tripeptide inhibitors led to the identification of the best moieties for each site: primary ketoamide at P', cyclobutylalanine at P1, gem-dimethylcyclopropylproline at P2, tert-leucine at P3, and tert-butyl urea as capping agent. The combination of these led to the discovery of compound 8 (SCH 503034, boceprevir), our clinical candidate. It is a potent inhibitor in both enzyme assay (Ki* = 14 nM) and cell-based replicon assay (EC 90 = 0.35 microM). It is highly selective (2200x) against human neutrophil elastase (HNE). Boceprevir is well tolerated in humans and demonstrated antiviral activity in phase I clinical trials. It is currently in phase II trials. This Account details the complexity and challenges encountered in the drug discovery process.     

Curing reaction of amino‐terminated aqueous‐based polyurethane dispersions with triglycidyl‐containing compound

Amino‐terminated anionic aqueous‐based polyurethane (PU) dispersion was obtained from NCO‐terminated PU prepolymer, which was neutralized with an excess triethylamine (TEA) and chain extended by ethylenediamine (EDA) during water dispersion process. That PU prepolymer was obtained from a polyaddition reaction of isophorone diisocyanate (IPDI), polypropylene glycol‐2000 (PPG‐2000), and 2,2′‐dimethylol propanoic acid (DMPA). This aqueous‐based PU dispersion was treated with trimethylolpropane triglycidyl ether (TMPTGE) as a latent curing agent and resulted in a self‐cured PU resin on drying. A model ring‐opening curing reaction between oxirane group of TMPTGE with terminal amino group of PU was demonstrated by glycidol with n‐butyl amine. The physical and mechanical properties as well as thermogravimetric analyses of these self‐cured PU resins were evaluated in this article. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Hybridization of aqueous PU/epoxy resin via a dual self‐curing process

Amino‐terminated and carboxyl‐containing polyurethane (PU) is prepared by an isocyanate‐terminated PU prepolymer process. Carboxyl‐containing epoxy resin is obtained from a half‐esterification of epoxy resin with maleic anhydride. These two aqueous resins are obtained after neutralization with triethylamine and dispersion into water phase, respectively. A latent curing agent (TMPTA‐AZ) is prepared by a Michael addition of aziridine with trimethylolpropane triacrylate (TMPTA). A self‐curing system of PU/epoxy hybrid is obtained from a blending of these two aqueous resins with latent curing agent. PU/epoxy hybrid is derived from two self‐curing reactions on drying. The first curing for hybridization between PU amino groups with oxirane groups of epoxy resin is via a ring‐opening reaction and the secondary curing takes place on carboxyl groups of PU/epoxy hybrid with aziridine of TMPTA‐AZ. The final properties of these dual self‐cured PU/epoxy hybrids are reported. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Electrochemical pitting behaviour of type 321 stainless steel in sulfide-containing chloride solutions

The pitting behaviour of type 321 stainless steel in sulfide-containing chloride aqueous environments was studied using cyclic potentiodynamic polarization. A well-established correlation between H₂S and Na₂S₂O₃ in the study of corrosion was applied, that is, H₂S was simulated by Na₂S₂O₃. The major factors affecting the pitting corrosion of type 321 stainless steel are the Cl^- concentration, solution pH and temperature. The results clearly indicate that both E_pit and E _pp decrease with increasing Cl^- concentration and temperature, while I _pass is more sensitive to temperature variation. E _pit decreased with decreasing pH in the range 2 < pH < 7.5. The surface morphology and chemistry of the corroded type 321 stainless steel resulting from anodic polarization in 0.01 M S₂O ₃ ^2- -containing Cl^- solution were analysed by XRD, SEM and EPMA. A higher concentration of sulfur was found in the pits, and the dark surface film was mainly composed of FeS and -Fe₂O₃. The results describe the pitting behaviour of type 321 stainless steel in sulfide-containing Cl^- aqueous environments.     

In Situ Confocal Raman Mapping Study of a Single Ti-Assisted ZnO Nanowire

In this work, we succeeded in preparing in-plane zinc oxide nanowires using a Ti-grid assisted by the chemical vapor deposition method. Optical spatial mapping of the Confocal Raman spectra was used to investigate the phonon and geometric properties of a single ZnO nanowire. The local optical results reveal a red shift in the non-polar E₂ high frequency mode and width broadening along the growth direction, reflecting quantum-confinement in the radial direction.