Theoretical analysis of the effects of asymmetric membrane structure on fouling during microfiltration

There is a growing interest in the use of both asymmetric and composite membranes for microfiltration and ultrafiltration processes. This includes particle removal applications in the semiconductor industry and virus clearance in biopharmaceutical applications. Filter fouling plays an important role in these processes. Although flux decline models have been developed for homogeneous membranes, the effects of asymmetric membrane structure on flux decline behavior remain poorly understood on a fundamental level. Here, we develop a theoretical model to describe the effects of asymmetric membrane structure on flux decline. The asymmetric structure was described by the spatial variation in Darcy permeability in the directions normal to and parallel to the membrane surface. The velocity profile and flux decline because of pore blockage were described using Darcy's law and a pore blockage and cake filtration model. Flux decline data were obtained using pseudocomposite membranes with highly interconnected polyvinylidene fluoride membranes (PVDF) and straight through pore polycarbonate track‐etched membranes (PCTE). Model composite membranes were formed by layering PCTE or PVDF membranes with different pore sizes on top of each other. Flux decline data for the composite membrane were in good agreement with model calculations. The results provide important insights into the effects of asymmetric membrane pore structures on flux decline. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Two‐dimensional electrolyte nature of exfoliated montmorillonite nanoplatelets fabricated by soap‐free emulsion polymerization and their affinity for cations

Montmorillonite (MMT) nanoplatelets, fabricated by the exfoliation of MMT during participating in the soap‐free emulsion polymerization of methyl methacrylate, were well‐dispersed in water and performed like a two‐dimensional electrolyte. Their ionic conductivity roughly follows the Manning's limiting law for the conduction of a polyelectrolyte. The dissociated MMT nanoplatelets that carry negative charges in water were able to rapidly adsorb cations, such as tris(2,2′‐bipyridyl)ruthenium(II) (Ru(bpy)) and methylene blue (MB⁺), and recover into a smectic configuration floating as a separating phase. By using the Langmuir equation, we were able to estimate the occupied surface areas of MMT nanoplatelets by each Ru(bpy) and MB⁺ cations as 4.708 and 1.806 nm²/ion, respectively. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Quantification of non-homogeneity from ocean remote-sensing images using two-dimensional continuous wavelet transforms

In this study, a two-dimensional continuous wavelet transform is applied to quantify the non-homogeneity from remote-sensing wave images. Our study shows that the non-homogeneity index, which is proposed here, is capable of identifying the degree of non-homogeneity from the wave-field images. However, the influence from the edges of the wave-field image should be considered in analysis. The calculated results from the simulated wave fields and from the natural wave-field images reveal that the non-homogeneity index is influenced by the bathymetry inside the area of the ocean-wave image. It conforms to the character of the natural wave non-homogeneity. After discussing the wave characteristics from the wave-field image with a high non-homogeneity index, an inhomogeneous algorithm is recommended for obtaining accurate and reasonable wave results from the wave image.     

Knowledge construction and misconstruction: A case study approach in asynchronous discussion using Knowledge Construction – Message Map (KCMM) and Knowledge Construction – Message Graph (KCMG)

This paper introduces a methodology for analyzing the knowledge construction and misconstruction processes occurring in online asynchronous discussion for Secondary 2 (Grade 8) students. The use of purposive sampling targeting specific students in a single course forum could potentially advance understanding of these processes using Knowledge Construction – Message Map (KCMM) and Knowledge Construction – Message Graph (KCMG). This paper traced the communication patterns and knowledge construction as well as misconstruction processes of students working in groups to formulate scientific ideas. This methodology reveals the dynamics of asynchronous discussion through mapping and quantifying the electronic learning process. This will equip educational practitioners and researchers with a useful tool for describing online interaction through adoption of a measurement methodology more systematic and effective than anecdotally. The research findings suggest that self-directed learning through asynchronous discussion has to be monitored by facilitators as learners possessed misconceptions that could potentially mislead other participants.     

Implementation of delta—sigma analog‐to‐digital converter in LTPS process

Abstract— An on‐panel delta—sigma analog‐to‐digital converter (ADC) has been implemented and verified for 3‐μm low‐temperature polysilicon (LTPS) technology with two basic blocks: a delta—sigma modulator and a decimation filter. From the experimental results, the digital output from the delta—sigma modulator is correctly matched with the analog input voltage ratio such that the digital output can be converted into 8‐bit digital code successfully under a supply voltage of 10 V from the decimation filter. The implemented on‐panel delta—sigma ADC can be used for the application of temperature‐to‐digital converter on glass substrate.     

Formation and characterization of diamond crystals synthesized by microwave plasma CVD system

Abstract

Diamond crystals have been successfully synthesized on (100) Si wafer using microwave plasma CVD. The growth was conditioned in a flowing system in which the parameters, such as CH₄/H₂ ratio, pressure, temperature and microwave power were varied. Cubo‐octahedra or tetrakaidecahedra are the equilibrium shape of diamond single crystals obtained under all conditions and are therefore the basic unit for the formation of polycrystalline diamond films, mostly through repetitive twinning and secondary growth of diamond crystals on {100} habit planes of cubo‐octahedra. Both X‐ray diffraction and Raman spectroscopy were used to facilitate the analysis of the diamond crystallinity and purity. These qualities are similar to those of natural diamonds.     

Structural Basis for the Improved Potency of Peroxisome Proliferator‐Activated Receptor (PPAR) Agonists

The need to develop safer and more effective antidiabetic drugs is essential owing to the growth worldwide of the diabetic population. Targeting the PPAR receptor is one strategy for the treatment of diabetes; the PPAR agonists rosiglitazone and pioglitazone are already on the market. Here we report the identification of a potent PPAR agonist, 15 , whose PPARγ activation was more than 20 times better than that of rosiglitazone. Compound 15 was designed to incorporate an indole head with a carboxylic acid group, and 4‐phenylbenzophenone tail to achieve a PPARγ EC₅₀ of 10 nM . Compound 15 showed the most potent PPARγ agonist activity among the compounds we investigated. To gain molecular insight into the improved potency of 15 , a structural biology study and binding energy calculations were carried out. Superimposition of the X‐ray structures of 15 and agonist 10 revealed that, even though they have the same indole head part, they adopt different conformations. The head part of 15 showed stronger interactions toward PPARγ; this could be due to the presence of the novel tail part 4‐phenylbenzophenone, which could enhance the binding efficiency of 15 to PPARγ.     

Methionine restriction up‐regulates the expression of the pi class of glutathione S‐transferase partially via the extracellular signal‐regulated kinase‐activator protein‐1 signaling pathway initiated by glutathione depletion

Understanding the molecular events underlying gene regulation by amino acids has attracted increasing attention. Here, we explored whether the mechanism by which methionine restriction affects the expression of the π class of glutathione S‐transferase (GSTP) is related to oxidative stress initiated by glutathione (GSH) depletion. Rat primary hepatocytes were cultured in an L‐15‐based medium in the absence or presence of 200 μM L ‐buthionine sulfoximine (BSO) or in a methionine‐restricted L‐15 medium supplemented with 20 μM L ‐methionine up to 72 h. BSO and methionine restriction time‐dependently induced GSTP mRNA and protein expression in a similar pattern accompanied by a decrease in the cellular GSH level. The phosphorylation of extracellular signal‐regulated kinase (ERK), but not of c‐Jun NH₂‐terminal kinase and p38, was stimulated by methionine restriction and BSO. Electromobility gel shift assay showed that the DNA‐binding activity of nuclear activator protein‐1 (AP‐1) increased in cells exposed to methionine restriction or BSO. With the ERK inhibitor FR180204, AP‐1 activation and GSTP expression were abolished. Moreover, the induction of GSTP by methionine restriction and BSO was reversed by GSH monoethyl ester and N‐acetylcysteine. Our results suggest that methionine restriction up‐regulates GSTP gene expression, which appears to be initiated by the ERK‐AP‐1 signaling pathway through GSH depletion in rat hepatocytes.     

Utilization of self-injection Fabry–Perot laser diode for long-reach WDM-PON

In this investigation we propose and demonstrate a wavelength widely tunable laser source employing a self-injected Fabry–Perot laser diode (FP-LD) for long-reach wavelength-division-multiplexed passive optical network (WDM-PON). By using a tunable bandpass filter and an optical circulator inside the gain cavity, a stable and single-longitudinal-mode (SLM) laser output is achieved. Besides, the proposed laser sources are directly modulated at 2.5 Gb/s for both downlink and uplink transmissions of 85 km single mode fiber (SMF) in PON without dispersion compensation.